I have done several "Dock Rash" repairs on my boat using the kit from Grady-White. As mentioned, you will likely NOT get a perfect color match due to sun bleaching. I use alcohol to clean the area around the ding. Lightly sand any rough areas with 800-100 Grit sandpaper and clean again with alcohol.Do ALL the prep before you prepare the gelcoat repair. Mix the gelcoat as directions specify. If you have more than 2 dings, you will need to work fast. The mix will began to setup within 5 minutes and will be un-workable within 8-10. I use masking tape around the repair to limit the amount of sanding do be done. Use a body filler spreader to spread the mix and get it as smooth as possible. Give the repair adequate time to cure and if you can allow it to setup over-night. I sand starting with1000 Grit then go to 1500 and finish with 1800-2000. ALL SANDING done with WET/DRY sandpaper that is kept wet. once you ge the desired finish, Wax, buff and repeat with 2nd wax coating.
IF you can see layers of fiberglass, you can cover up to one layer of glass. Beyond that, you might need professional help. If so, find someone working on Corvettes that does body work or someone that knows thier stuff doing boat repairs.