My drive belt flew apart an knocked a hole in the top of my tank, managed to get the piece pryed back up into the hole so its flush now. Couple small chunks missing, about the size of 1/4 in bolt. Can I use a fiberglass kit to patch it or will the gas eat it? Some body told me to try jb weld for plastic

Get some Seal-All. You may have to put something over the holes to use as a bridge because it is pretty thin but it is resistant to gasoline.