Would use White Marine-tex is all it needs to fix it. No fiberglass resin or fiber needed.
get a plastic putty knife to apply it as smooth as possible so you have less to sand once it cures.
some light grit sand paper, to finish it up after it cures.
use plastic gloves while working with this and a paper mask when you sand it also.
1st would wash area with acetone, light sand and knock the loose chips off the area to be sealed up.
2 after it cures put a coat of wax back on the areas as the acetone will take the wax off the areas you use it on.
Would highly recommend putting a keel guard or hamby beaching bumper on your boat also to protect it in the future.
Flex seal might work but I would not try it on my boat, lol
went and picked some up today at North Shore Marine. Got it put on and gonna leave it alone till Wednesday to fully cure good before final sanding, if even do that. Not really worried about looking perfect as long as does the job. Used the extra to just fill in other small gashes on bottom. $18 bucks for 2oz kit so wasn't that bad, I was out of resin so would of had to buy some of that anyway.