That's the kind of memory that could be a painful "what if" had you not got the courage to ask her to prom. Small but critical details like that are everywhere in our lives and they as a collective make up who we are. As you get older you realize you can't miss your opportunities in life. OP, at the very least try and keep in contact with her so she's not a fleeting "what if" memory in 30 years and maybe you have a wonderful one like this.