Underwater epoxy putty suggestion, and tips

I have a crack in the bottom of my fiberglass pool. The quotes to fix it have been between 3-5k. It's just not something I can afford at the moment. As the title states I need to apply it underwater. Is there something that anyone has had good luck with? If so are there any tips on applying it to get it to stick well? I was not sure if you should rough up the area around the crack before hand? I am hoping to get through the summer season, however I do know it's only suppose to be a temporary solution.

It's also a fairly long crack (about 12 inches) and one side kind of sticks up a bit over the other. Not sure if I should shove it full under the small lip, or just smooth it over the top.

Thanks