I think you'll find there's no one "correct" way (or two ways, or three, or ten).
Everybody figures out what works for them. There are many ways to balance between outlining and improvising, including:
- Writing an outline as a starting point, then feeling free to diverge from it, to the point that the final product bears no resemblance to the outline.
- Pantsing the whole thing, treating that as a rough first draft, and then writing an outline that's clear and well-structured in advance of your next draft.
- Writing an outline that's full of holes and gaps, to be pantsed in during the process (e.g.:
"[Something devastating] happens to main character here, and she leaves the agency! She's also growing increasingly intrigued by Jack, after she spots him [doing something suspicious; figure this out once I know who Jack's actually working for]")
- Writing an outline for the primary plotline, but establishing multiple side-plots without any outlining.
- Switching back and forth from outlining to writing; whenever you feel like you're veering away from the outline, you go and change the outline to account for the changes you want.
The point is this An outline is a tool. It's a tool that gives you some sense of where you're headed; that lets you look at your story at a macro level. Knowing where your headed is particularly powerful because it makes your writing more purposeful; it gives you very specific goals to move towards; it gives you grounding in details the "reader" doesn't yet know.
But it's not always the right tool for the job. If you're feeling like the story doesn't interest you, then knowing exactly what the end is going to be might not be the right tool. If you're focused on making the story energetic and exciting, then focusing on moving the story along to the next plot point is not helpful. If you have no idea where you're headed, then striking out in some random, enticing direction may be much more helpful than trying to plan your entire route before you've taken a single step.
There is no problem at all with mixing between the two. Every author does, finding the mix that works for them (which may well be different from project to project.)
At every point, you just need to figure out what you need next. If you need firmer grounding and clear direction, go outline. If you need to sit down and get some words on the page, or to play around with some of your characters, go write. If you have no idea, pick one, see if it works; if it doesn't, go do the other.
With time, you'll find your rhythm, your preferences, the way you're most happy using your toolbox.