I like the wax paper technique for dealing with scratches and chips.
Clean out the scratch or chip with soap and water, let dry.
Scrape out any loose or oxidized gelcoat with a sharp tool.
Vacuum clean. Mix enough gelcoat of the matching color and hardener
to fill the chip or scratch, then fill the damaged area with it
to the same level as the original finish. Then tape a section of
waxed paper tightly over the repaired area to smooth and cure the new material.
A clear overhead projector sheet works better if you can put your hand on one. The thickness makes a better press and the inherent static sticks real nice to the hull and really feathers out the gel coat nicely.