I'm working on a 2-piece poplar guitar body and I'm in the final sanding stage before applying finish. I've sanded the body all the way up to 320 grit and yet I have spots that are fuzzy (don't know how better to describe this). The problem is more pronounced in the greenish parts of the wood. Surely 320 is more then adequate grit to apply finish to, so I was wondering how can I fix this issue? Should I keep sanding the problematic spots to higher grits?