AITAH for getting revenge?

I I'm in the friend group and they have all been friends for a while. I joined about 2 yrs ago. Everyone was all good for about a year only small fights here and there. One night in the group chat there was a fight. The main member of the group was being mean to another one who has bad mental health and I knew she was bad at the time she was texting me crying and so I stood up for her in the group chat. One of the girls didn't like me for that the day after at school (she dih rides the main member of the friend group) and started being slightly mean to me. It progressed everyday till she would tell me to kms and call me fat daily. Ive had enough of the constant bullying and no one in the group doing ANYTHING about it so I planned revenge! It was only on the bully tho. Anyways what I did was write a note say all of the nasty things she's done to me and then when it was a passing period and the halls were super busy I dropped it. Immediately a group of guys picked it up and read it. Then they spread it a round the whole school and asked her about. She later texted me that she was sorry and I had ruined her reputation. I started to feel bad but then the next day she was still being a bitch to me so I don't regret it. Anyways no one even talks about it anymore and she got a new friend group. I feel like I shouldn't have done that but its not that big of a deal I mean she did make me fall into depression soooo.... AITAH?