As others have mentioned, it seems like you may have written a synopsis rather than a full-blown novel.
That's a great first step and a skeleton for your story.
If you haven't already, divide your story into scenes. A scene is usually something that takes place in one location, at a specific time, with a set number of characters (a few may exit or enter, but too many and you may have a new scene).
At it's core a scene consists of this (among other things scenes can do):
- A main character with a goal
- A POV character (usually the one with the most to lose in the scene—most often the same as the main character)
- Opposition, usually from an antagonist or several
- Then most scenes should end in some kind of setback
- All scenes should turn
Just adding opposition to your scenes will expand them. When the main character doesn't get what they want immediately, the scene will take longer, but opposition also adds drama and makes it interesting to the reader.
Having opposition also means you need to explain it. Characters opposing each other for the sake of opposing is problematic. Telling the reader "Q opposes W because of R" is not going to go over well with the reader. You may have to add scenes that show the reader why Q opposes W instead.
Having the scene end in a setback is also a sure way to expand the story. When going from A to B has to be done through C, D, and E, the story expands. After all, if the character goes from A to B with no problems or issues the story reads more like a project manager's success story than a dramatic work of fiction. (Imagine what would have happened to world literature if Homer had just done "After the trojan war, Odysseus went back home. There his loving wife waited for him with a hot meal and a stiff drink. End of story.")
Always ask, what could go wrong here? How can I thwart the main character's ambition? How can I send them astray?
Doing that will generate a bunch of new scenes. Getting the main character back on track again (to B) will generate a few more scenes... (Unless, where the story is going now is way funnier than going to B, then you may have to go with the flow instead... perhaps you'll eventually find your way back to B or someplace that is B-equivalent anyway...)
Having a scene that turns, if you didn't check the linked page, means that it introduces some kind of change. Once the scene has played out, the world, the characters, the story, or all three have changed somehow. If the scene previously did not turn, you're likely having a couple of problems you need to write yourself out of now...
Once you have a scene with a goal and opposition, it's time to visualize it.
Close your eyes, take a deep breath, and imagine the scene playing out in your mind.
See the characters as they act, talk, and move. Pay attention to:
- Actions. What are they doing? How do these actions help the main character get closer to their goal and how do they help the antagonist thwart it?
- Reactions. Then look at reactions. Never have an action without a reaction. Just like you should never have a reaction without an action. How do characters react? Does that send them spinning out of control? Or do they try to keep that control so much that they have to do something extra? Get a drink? Put a pin in it and go meditate? Etc.
- Setting. How do they interact with the setting? Do they pick things up? Lean on things? Brush things off? Shield themselves with objects? Wield them as weapons? Where in the room (or place) are they? Standing? Sitting? Lying? Moving? Stationary?
- Dialog. What are they saying? How do their voices sound? Do they say what they mean and mean what they say or do they have subtext?
- Body language. What do they do with their hands? What are their facial expressions? Eyes? Mouths? Foreheads? Jaws? Necks? Backs? Legs and feet?
How do these factors change when the scene progresses? How does the main character react when they meet opposition? How do the antagonist act when they oppose the main character?
How do these factors differ among your characters? How expressive are they? How verbal? How active?
Do you have all that?
Good, now put it down on the page. Get it all down and worry about overdoing it for the editing. You can always cut something that is on the page. Not so much the other way around.
Also, don't worry too much about explaining it all. Not right now. In editing, you could always figure out what that twitching foot really was all about and may find you should add or remove something to make the emotion of the character cohesive, but right now you can just play with it and have the characters try their bodies, the setting and the scene out.
Speaking of editing, I've found these variations of how to do that:
- Edit each chapter after you've finished it
- Stop at 10 000 words and do an edit
- Edit each time you've written 10 000 words
- Write the whole draft, then edit it
Did you also ...
Other things you may or may not have in your manuscript that would expand it:
- Descriptions of characters. You should have at least one paragraph for each character the first time we see them, but then you might continue describing changes in their appearance. Maybe some of them are so colorful they need some description every time they enter the page...
- Descriptions of settings Each scene should begin with at least one paragraph of setting description, and then you stay aware of the setting as the scene progresses for instance by characters interacting with it in different ways.
- Character arcs. An arching character is someone that evolves and changes with the story. Having character arcs add the need for scenes to show this change or characters to help or thwart this change. Character arcs are also a fundamental element of story and in essence, either your main character changes or they causes other characters to change. A story without character arcs often feels thin.
- A three-act structure. If you count the three acts of the three-act structure as beginning, middle, and end, it can be said all stores have them. If your story does not have all the elements of a structure like the three-act structure or other structures it could feel half or uneven. With them, you need to add scenes for instance for plot points, the normal world, the new normal, etc. The three-act structure can also help pinpoint where a story might need to expand.
- A subplot. Subplots can do many different things from adding romance, theme, deepening character, etc.
- Theme. The theme of the story can come to you later or be part of the initial idea. As long as it's weaved into the story subtly it will add depth. Having a theme might raise the need for a subplot, add substance to minor characters, and may help to expand the story via story questions. You could also use motifs to show theme. Using motifs may also add the need for descriptions, even characters, settings, or scenes.
- Voice. Working with your narrative voice as well as character voice will most likely expand the text some. (See "VOICE: The Secret Power of Great Writing" by James Scott Bell).
- Characterization. Working on deepening the characters will most certainly add both scenes and text to existing scenes. When you start writing about not only what the character does, but also how and why, things start adding up. (See "Writing Unforgettable Characters: How to Create Story People Who Jump Off the Page" by James Scott Bell)
- Dialog. Deepening and sharpening the dialog will likely expand it. Reading up on dialog may also give you ideas on how to use dialog instead of narrative description. Dialog is one great way to show instead of telling. (See "How to Write Dazzling Dialogue: The Fastest Way to Improve Any Manuscript" by James Scott Bell)
Keep things complex, not complicated
Another way that may or may not expand the novel is to do all of the above while not making the story complicated.
You could think of a story as "complex" or "complicated". We want "complex", we want to avoid "complicated".
In essence, complicated is when you have many different threads and pieces and they don't fit together, but rather go off in all directions.
You could think of your story's elements as cogs and cogwheels. "Complex" is when all the wheels connect and you're still able to make them turn. "Complicated" is when they do not connect, or connect in such a way that they cannot be turned.
Making a story complex could involve adding elements to make the parts connect. It may also mean cutting some things out.
Keeping an eye out for complex vs complicated is a great way to coordinate all additions. If it makes the story more complex, great. If it makes it complicated, you may have to reconsider.