I was afraid the answer was going to be more sanding

I find my sandpaper gets gummed up with poly quickly, so I could wet sand with 800, but I'm not sure if that would be the right approach at this point.

It's possible that I added more layers too fast, I was doing about 3 a day because it dries so fast. But also the veneer was not completely flat, so the bumps could just be from bumps in the veneer.