AITA for refusing to lend my sister my prom dress?

I (23F) graduated 5 years ago. My prom dress is still in great condition and I have worn it several times since my prom.<br><br>My little sister (18F) is now looking to attend her prom with her long distance boyfriend.<br><br>She asked me if she could wear my prom dress and I said yes but when she tried it on and I saw that she was going to need some alterations for it I changed my mind. I don’t want my prom dress to be altered because I am planning on wearing it again in the future. <br><br>I told my sister she had to find something else to wear and gave her some suggestions for nice and cheap dresses which she can use instead. She was very disappointed when I told her she couldn’t wear my dress.<br><br>She went and told my mom on me and when mom asked me why I wouldn’t lend her my dress I said I didn’t want the dress to get ruined with alterations. My mom yelled at me for being self centered and told me I don’t need that dress anymore since my prom is over so I should lend it to my sister.<br><br>I had to spend the rest of the night alone in my room since my mom and sister were mad at me.<br><br>AITA for not wanting my dress to be altered?