oppps theres a two holes in my fiberglass fuel tank

After the tank is fixed, you might re-locate and re-drill the holes in the fins. Maybe then you can put them where you want without problems.

 

I'm still unclear as to whether the bottom of the built-in fuel tank, and the bottom of the boat, are one and the same. If they are, I'd be looking at rather large, stainless, closed, blind rivets as a possibility, You'd need to talk to a specialist fastener supplier as to availability. Especially if you could get inside the tank to position a decent stainless washer as a backing plate.

 

Looks like the fuel is indeed contained by hull and sole.

 

This is exactly why in the USA (EU, and Canada as well) integral fuel tanks on gasoline powered boats are prohibited. Non-integral tanks are far safer and there is not the risk of a spill. I would echo the suggestion that you get rid of the integral tank and install non-integral tanks.

Also I might add that fiberglass is not a good material for gasoline tanks. There have been significant problems with fiberglass tanks leaking. Some of the components of gasoline are destructive to resins used in fiberglass. Gasoline (as I'm sure you know) is an excellent solvent.

 

It depends on the resin used, isothalic polyester seems OK.