It's probably just the fish, not your fault. That sucks, I'm sorry. My fish wouldn't eat when I first got him, which brought me to this forum and I realized that the bowl I had him in was a bad environment for him. I switched him to a heated 2.5 gallon tank, and he was suddenly eating, flaring, and bubble nesting.
It sounds like you are a responsible owner and did research though, so it is likely the fish is less hardy than others.
I hope he makes it, but if not, don't give up if you think you can handle another one. There's a MUCH better chance that they'll die in those cups than they will with a loving owner. :)