I have outlined my story: plot, characters, setting, etc. but there are gaps in my story; do I keep writing or do I plan it out first?
I'm not completely sure what you mean, but do note that plot holes are actually inconsistencies within the plot, not when your story is literally missing parts. That's just an unfinished plot. At any rate, since you have already been outlining the story, I would recommend you complete the outline first. You don't have to, but the whole point of an outline is to ensure that the plot makes sense before committing to writing it. The last thing you want is to be fifty thousand words deep into the story only to find that you made a mistake forcing you to change your plans and rewrite large amounts of text. That sort of thing tends to be kinda disheartening and makes you lose momentum. This is especially true if there are actual gaps in the story where you're not even sure what's supposed to happen. Again, it's possible to simply wing it, but it's risky.
My first novel, which I'm still working on bringing to final draft status, was drawn from an outline I thought was finished but wasn't. Don't get me wrong. I worked hard on that outline and included every major plot point and plenty of minor ones too. I left gaps though. I thought the rest would fill itself in. "...and yada yada yada, they fall in love." That sort of thing. Unfortunately, those sections where my outline was skimpiest ended up being some of the hardest parts to write. Worse, I ended up with a 60k book when I was finish, about 20k shy of recommended length for a novel. Everyone who's beta read it for me says it's very well paced. The consensus seems to be that if I add 20k here and there, that I'll lose that pacing. I don't know what to do with it. My new novel has a much more in depth outline. I know what's going to happen at every intersection and every point in between. Plus, I know it will definitely hit 80k if I follow through. None of this means I can't improvise. I'm only a chapter in and have already surprised myself several times. What it does mean though, is that I won't have to fill in major moments on the fly or sit staring at my computer trying to come up with enough material to fill a months long gap. What this question comes down to is, are you an architect writer, a discovery writer or a hybrid? Hybrid writers start with an outline and improvise all the way through it, sometimes going so far off book that they end up with an entirely different story that the one they intended to write. Will you be able to fill in those gaps as you go? Only trying will tell.
So long as you're writing you are making progress. Though sometimes if you don't stop and think/plan about what you're writing you will make bad progress that will cause larger problems later on. It's an age old dilemma with no easy way out.
As noted, if there are gaps in your story, fill them in in outline. Personally, that is why I am such OCD with worldbuilding - world itself tells the story. So look at where those holes originate: is it the story itself, or characters, or setting? Then you will know what you need to fill out.
Write. As you gradually transform your outline into actual text, ideas will come to you and you'll know how to fill out the gaps.
Write it with the gaps. And I say that because gaps are a lot easier to fill in, when a person knows where their story is headed. Because often times I find myself filling in gaps only to find I just filled in the wrong gap.
