Why do you believe it damaged your gas tank? About the only thing I can think of is you had a fair amount of water in the tank and not too much gasoline. If that is the case, all you need do is to fill the tank with fresh gas and it should improve. Next tank full add a can of water absorber (HEET) and by the end of that tank full everything should be fine.
Why did you add whatever you added to the tank?
BTW I have never heard of "gas anti-freeze" I am guessing it was a treatment like HEET used to absorb the water in the tank and run it through the engine. It you have a lot of water the engine will get rough and may even stop. Gas does not freeze, only the water in the tank. You should not have any water in the tank so normally you don't need to add anything to the gas that comes out of the pump.