Do I need to return my tiger barbs?
I recently purchased 12 tiger barbs for a 20 gallon (long)... Before you get upset; that was not my intention. I went to the fish store intending on purchasing a dozen unique guppies but they ended up being more expensive than I anticipated so I had to change my plan :/. I decided maybe I could stock it with something else and asked one of the workers about the tiger barbs, a fish I didn't previously know too much about, and he said it would be "totally fine" if I kept 10-15 in my 20 gallon. It should be noted that this is an aquarium store, not some big big brand pet store. Upon returning home I decided it would be best I do some more research and was very unhappy to discover the sizes they can grow to. They have been in the tank for roughly 7 hours and are young (no bigger than 2cm or 2 thirds of an inch). I regret not doing more research beforehand and seem to have made a mistake as most sources I read say roughly no more than 5 should be in a 20, and its best to have them in schools of 7-8+. There are also 3 panda corys and 2 clown plecos, all of which I intend to keep.
Bottom line; should I be returning these fish?
I am relatively new to the hobby and do not want to start mistreating fish accidentally.
Thank you very much,