Should I keep this dress or buy a new one [please read]?

For the farewell dance at my middle school, I went out and bought a dress and returned it the next weekend because I didnt feel it was formal enough for the dance. In this same weekend, I bought another dress from Charlotte Russe that I compeletely fell in love with. I thought all of my dress worries were gone until I found out that two girls in a grade below me had worn the same dress on several occasions such as their own dance (they won't be at my dance). A few people from my grade noticed this. The whole time I was dress shopping I really wanted to avoid buying the same dress as someone else. Do you think its worth the hle to go and buy a dress for the third time so I have an "original" or just stick with this one and ignore the fact that someone already has it?