It has been very sad to read this thread as through no fault of your own you are being told you have brought these fish into unsuitable conditions which will lead to them living shortened and possibly unhappy lives.
The posters are all correct and they would all like the best to be done for these fish, but the fact is the vast majority of goldfish passing through the pet trade lead very short stressful and possibly painful lives before they die in some totally unsuitable bowl. It would be best if the aquarium trade were unable to sell them to the general public, but that never going to happen.
Which brings me to these 3 specific fish. Would it be best for them if they were returned to the aquarium shop and left to an uncertain fate (and I think we could guess what that will be!), or with your new knowledge could you not provide a environment which, whilst not optimal, would give them more comfort and contentment throughout their (shortened) lives.
You are obviously quite young, but also very caring, and it is a difficult decision to make. It is something nobody would like to have thrust upon them. But that is life.
Do bear in mind that things can change and possibly you may be able to get a larger tank in the future or maybe you may move to a house with a pond, which is probably the beast home for a goldfish.
Good Luck.