I had a 1976 Macgregor fiberglass sailboat for 4 years when I lived in Hawaii, I just used home depot cloth, but make sure you use epoxy resin, its more expensive but worth the extra money. Make sure you wear a filtered mask when sanding, and sand that area and repair it with the cloth/epoxy. The inside looks fine but you could smooth it out if you wanted to. make sure you paint over the repair as epoxy and UV rays don’t get along well over time. I use marine grade only on outer hull, but you could get away with latex exterior acrylic on the inside and save a few bucks. Its hard to walk you through fiberglass repair just by writing, but there are many videos on youtube repairing boats/surfboards etc. You should at least watch a couple before you have a go at it if you haven’t done it before.