welcome to AC!
for the best life for the fish, you should really look into getting a real fishtank, instead of just a bowl. it is a big myth that goldfish can live in a bowl, or that they will only grow as big as their "home". pet stores, carnivals, and even tv continue to perpetrate this myth (ever watched west wing?)
truthfully, goldfish need at the very least a 20g tank for one fish. 30g would be better. in a proper home they can live upwards of 12-15 years, while in a bowl they *might* live for 3 or 4, if it's a big bowl. instead of growing, they die. i don't think you should feel bad about the goldfish - we have all made that kind of mistake based on false information we were given, whether it is this kind of situation or a betta fish in a vase, etc., but you should either try and get a bigger tank for it, or find a home for it with people who have a correctly sized tank. a fancy (round-bodied) goldie can reach 6-8 inches long, and the common (long) goldfish like the kind found in carnivals, classroom experiments, and used as feeder fish can reach 12-14 inches. i've personally seen a couple of fancy goldfish as fat around as a 1-liter soda bottle.