more matting on weak spot

yes you can. just sand the paint and primer away from the soft spots make sure to get to the fiberglass. also make sure that you sand the spots 2-3 in. wider all the way around. make sure to use 40-80 grit sand paper so the new resin can have a good hold. put a thin coat of resin add fiberglass then another thin coat of resin. do this 2-3 times. if it is in a spot where you dont want a small hump then you can go wider and fether it out . to give it less of a hump. then use body filler to cover the sanding marks. then sand, prep, prime, and paint.

p.s. always use the thumb test before paint trust me it will save you time and money. thumb test you say??? press your thumb all around you project firmly this way you find the soft spots before its to late.