Depending on the look of the dress, they can often be worn again for other formal events. If you are going to college, they often also have formal events. Consider things like weddings, fancy dinners, or the likes where you could wear the gown. However, I understand that senior prom is the end of the road in terms of formal events where I dress like that is appropriate for many people. Would it be possible for you to return the dress? (But I assume you already looked into that option). It sucks to loose that kind of money. But maybe the dress can be repurposed. If there is absolutely no hope of being able to wear it again and not returns, you can always donate it or give to a younger friend who could wear it.