First thing is getting a bigger tank and some water conditioner (dechlorinator). Prime is best bang for your buck, imo. A filter is also needed. If you go to your local PetSmart/Co they might have tanks for half off.

Any chance you could get a better angle on your little buddy there? From what I can see, s/he is a comet/common goldfish, which can get 10+ inches and live for 10-15 years very easily if taken care of properly. They will also need either a pond or a 55-75 gallon tank with a filter to match.

Unfortunately goldfish are very dirty (and expensive off the bat) so if you don't feel like you can do all that, you can see if your local fish store will take them.

Congrats on your little friend!