Don't paint… the boat is fiberglass, use the appropriate materials. Paint will scrape or peel off (80 grit paper will make scratches you can see from 50 feet). You may be able to sand and polish the gel coat back to its original condition. Start sanding with 400 go to 1000, then 3m polishing compound. Any voids should be filled before final sanding. If gel coat is to thin for sanding re-coat with quality polyester or epoxy.