Thanks for the advice.

I ordered a touch-up pen as well as assorted colors of wood filler. I'm optimistic that at least one of these will work.

Yeah, it's a shame that this happened but from what I've read of others' experiences it could be a lot worse. Since this is my first build I accepted from the start that I'd make mistakes. I'm keeping a personal record of all of the things that I'd do differently if/when I make another attempt. Maybe I'll share it when I'm done.