AITA for buying something someone had already "claimed"?

So I (22f) was at the store with my fiance, and I saw a really cute bikini. I tried it on and it fit perfectly, so I decided to buy it. When we were getting ready to leave, one of the store employees came up to me and said that the bikini I was carrying was a "display" bikini. Apparently display items aren't to be taken, and since they were short on staff, they need mannequins with clothes for display. <br><br>I apologized and said sure, whatever, and gave it back to the employee. <br><br>When I got home, I posted on my IG story about what happened. My coworker (let's call her Lila) saw that post and DM'd me saying that THAT EXACT BIKINI was what she had been looking for! Apparently she went to the same store looking for it, but it was "claimed" by someone who already paid for it and was waiting for it. Lila said that she asked if she could buy it off her, but the girl said no because she paid for it already so it's "hers". <br><br>Lila was really upset over it, and I felt bad for her. I told her I'd keep an eye out, and if it's still there the next time I go to the store, I'll buy it and send it to her. <br><br>Fast forward a week, fiance and I are at the same store, and I see the same bikini. It's still there! I was so happy for Lila, but just then, the same employee comes up to me and says the same thing as before. I was like "no, I bought this last time and you took it from me." And she was like "oh yeah, I'm so sorry. You're right." <br><br>I believed her and thought nothing of it, until the girl who "claimed" the bikini approached me, saying that I couldn't buy it because she ALREADY BOUGHT IT. I was like "no, I'm buying it now, you can't buy something that isn't for sale." <br><br>She got mad at me and called me an asshole for buying something she already paid for, but I didn't back down. <br><br>Am I the asshole for not letting this girl have the bikini that she already paid for?