Gaps forming along walls, after DIY install

Q: Recently I installed oak hardwood floors in my house. I used pneumatic nailer, but at the area close to walls I had to nail down manually, and I can see gaps between woods.

How do I fix this problem?

A: As you got near the wall, each board and each row should have been pulled in tight, either with a pry bar or floor jack, if you are lucky enough to have one of those. Now, you would have to take up the rows in question and re install them tight, or fill the gaps with any commercial filler that will match.