Yes, I agree with the previous post. You really should get a bigger tank, a 5-10 gallon, or even 20. This also means you will need to buy a filter, heater, water dechlorinator, and substrate, decorations, and air-stone... the last 3 aren't necessary, but the fish will only benefit from them. Substrate and decorations makes the fish feel more comfortable, and allows places to hide, and air-stones provide water movement to the surface which increase oxygen levels.
I'd also pick up a liquid test kid, for ammonia, nitrIte, and nitrAte. It's up to you if you want to spend the extra money...this will let you know how well your water quality is.