I am very sorry and its not stupid to get upset of fish I still get upset over fish. I think that becuase you tried so hard to save him proves that you are a great fishkeeper. If your worried you can dry the tank out for 48 hrs. The heater thermometer anything glass is probably fine because its non porous. Anything bad should evaporate or die off. And sense you didnt have the tank cycled you wouldnt have to worry about that. Depending on where you got the heater I would go in and complain at least they could do is just replace the fish and the heater for free or refund your money. Any good store will because they want your service.
Go in and try to barter with them I have found fish that are obviously ill (velvet or ich or bloated and floating due to bad practices) but something treatable and I can get a discounted price and that way they loose some money I have gotten fish for about half off :) just because they were overfeed and floating. But if you really dont want to give the chain stores money. You could probably find someone online here who might be able to give you a great deal.