Check to see if there are tub refinishers in your area,( such as Perma Glaze), to get estimates on the repair. Repairs before the re-finishing is typical on acrylic, fiberglass, and even porcelain veneered tub/showers.

Refinishers as mentioned by sierraeast would do the job so it would be nearly invisible. If costs are an issue, you can do it yourself but unless you do a lot of practice work first, chances are it will be noticeable. The hairline crack indicates there is some give that needs to be addressed also. A good patch is stronger than the base product which means a new crack may eventually show up nearby. The cause of the flexing can be fixed in several ways, some elaborate, some not so drastic. It depends on the situation of your installation.

I'm trying to diagnose a leak from a fiberglass tub area. It's proving challenging because there are multiple spots under the tub that appear wet, yet when you see the inside of the tub, there is no apparent damage. Particularly I see water stains on the outside of the tub about 20 cm below where the tub spout is. The tub spout was not finished flush with the fiberglass, and the caulking has failed. I re-caulked it today. But the drip marks were not immediately around the hole for the spout. The white water stains have drip marks to the ground and the floor under the tub is soaked. But I also notice water actively getting through the tub where the tracking is for the shower door. Just in the one end of the outside of the tub which I have exposed, I saw 2 more wet spots. Does fiberglass sometimes get multiple pinhole leaks and cracks which are hard to see?