before i sand/scrape i use clear fingernail polish,if you have a prop that is much more out of balance than that like was said trash it.if you do sand i have done this,all the prop manufactures recommend sanding or applying any coatings to the front outer sections.here is what master airscrew says about them.
http://www.masterairscrew.com/techbull.asp#F

this is from zinger,i think wooden propellers though.

http://www.zingerpropeller.com/Ballance.htm

hope this helps...happy flying