Any good short story needs conflict. Since you are evidently a young female student, it seems to me that you could write an effective story about a conflict involving young love. For instance, you might write about a girl who has two very different young guys in love with her and she can't decide which one she wants to go steady with. That would give you the three characters you need, and there would be plenty of conflict because the girl would be experiencing an internal conflict while there would be an external conflict between the two guys. One of them could be an athletic type and the other an intellectual, just for example.
Another conflict could involve two girls who both fall for the same guy. They might be good friends, even roommates, but become enemies when this guy comes into their lives. This would be a Jane Austen type of plot. One of the girls might be a cheerleader type and the other an intellectual type.