Hi! My first post here. I'm doing my first set neck refret - a LP Standard. When I lay a notched straight edge over the treble side, the neck is perfectly flat. When I lay it over the bass side, it has a slight backbow, with the apex at the 9th fret. Rocking the straightedge towards the body end, i can fit a .009 feeler gauge under the straightedge at the 1st fret. Rocking it towards the nut, I can fit a .011 feeler under the straightedge at the 22nd. I should be able to sand this out without losing much fingerboard thickness, right? Anything else I should try that?