Do you find your first draft is longer or shorter than your completed work? I understand that I will be cutting alot of unnessary words, but I also have a list of things I need to add. I haven't gone back to add these in yet. I'm finding it difficult to know if I'm doing okay with the word count. Is it okay and normal for it to be lower than than the final piece?
I think this is a matter of personal writing style.
My first drafts are typically shorter than my final drafts; even though I cut entire pages out of my first drafts, and in one case ten consecutive pages were rewritten into half a page. (In the first draft, I had a plan for a secondary character that didn't work out, it just didn't fit right. I deleted him and his introduction and dialogue, and the slack was taken up with a different character.) I also cut any unnecessary exposition, if it feels boring I rewrite it.
However, despite all that cutting, as I re-read scenes, I often consider them under-imagined, without enough imagery, color (literally color of the scene being described), feelings or emotional context, and so on. I see places where my dialogue is too blocky; just people talking, and that needs to be broken up with some stage craft, action, pauses, thinking, and so on (a wall of dialogue is an under-imagined scene; people DO things as they talk). So I fill them in.
That makes the story read and flow better and it increases the word count; often by 20%. Although you need to hit some minimums to have a novel, I wouldn't worry too much about word count. Write and rewrite until the story reads smoothly to you, cover to cover.
Which is how I rewrite, cover to cover; it gives me enough time between revisiting scenes so I see them with fresh (and more analytical) eyes, so I can tell if they are boring, or awkward, or need work. For me, usually by the sixth draft I read through the whole thing without a hitch, then I'm done and its ready for the next step. I don't limit myself to six drafts, my first book I probably did 20 drafts before I was satisfied. But now six is typical.
Word counts are dangerous. Very dangerous. The reason is that you have an element entirely alien to the creative process (as well as external to it) which takes over.
Indeed, I was talking with someone the other day about a well-known TV series (doesn't matter which; they all fall for the same trap) which was supposed to be 1 season, then it became 2 and now there are plans for more. Ironically enough, it's based on a book and the events described in the book are already dealt with in season 1.
Can you imagine being a writer of a TV series, with some producer over your head telling you, "I don't care what you'll do, make me episodes that don't resolve anything for as long as I tell you. Then, I want you to wrap things up in 8 episodes."
Obeying a word count blindly is a similar trap. Now, the operative word here is blindly, There are indeed purposes in having a word count, mostly marketing ones though, but perhaps it can also be an indicator for less experienced writers as to whether their story has come full circle. If you think you're done with 30.000 words, something probably isn't right.
So, to answer your question after this long but necessary detour, a first draft is basically a very extended outline of the story. It helps you visualize what's there. Now comes the next step, formulating the story into a narrative, which is an entirely different animal. It doesn't matter how long or short the first draft is. Some things will have to go, some things will have to be added. If your final draft word count varies by more than 25.000 words from other works of your genre, then you could perhaps ask yourself whether you've been either too laconic or too verbose. But certainly not before the final draft.
Many professional writers and editors report that there is about a 25% loss between the first finished (!) draft and the final draft.
Depending on your approach (e.g. either outlining or pantsing) and your experience as a writer (is this the first book you write and you have to find out how to do it as you go along, or do you know the next steps?), your very first draft may be very different from the first finished draft, or it may be the first finished draft.
Since you plan to add in material, it seems to me that you are both inexperienced and didn't plan your story beforehand (at least not in detail), which makes guessing the final wordcount rather impossible.
Please not the difference between "first draft" (which is the first version of your story that you write) and "first finished draft" (which is what you send in to your editor or agent).