Hi savo318
While corys like the company of their own species, I wouldn't worry about the julii. It will get along fine, but if you have the room, it would be good if you can get another like him. This would be a better alternative, IMHO, than bagging him up and taking him back to the store to be sold again.
It's also possible that the C. julii was mislabeled and is actually a C. trilineatus. This is more often the case than not. If you post a picture of it, I'm sure someone will be able to identify it for you.