AITA for refusing to help my friend last minute and “ruining” her night?

I (18F) feel like I’m losing my mind over this, so I’m here for an outside perspective.

I live in a boarding-style setup where we all share common spaces, but everyone still has their own rooms and schedules. I had plans made days in advance to go out with a group of friends. Everyone was already waiting on me, dressed, ready, and on a tight time window.

About 10 minutes before I’m about to leave, one of my friends (also 18F) texts me asking if she can drop her bag in my room because she “doesn’t want to walk back to hers later.” Important detail: I could literally see on Snapchat that she was still sitting in the cafeteria. She wasn’t rushing. She wasn’t on the way. She just assumed I’d accommodate her.

I replied honestly and said I was already leaving and couldn’t wait around.

She immediately got passive aggressive, saying things like:
• “Wow okay, I guess I’ll just struggle then”
• “Didn’t think it would be that hard”
• “You could’ve helped if you wanted to”

I didn’t snap back. I just reiterated that I had plans and people waiting on me. She then stopped responding.

Later that night, I find out she was telling people I “left her stranded” and that I “care more about going out than helping a friend.” Now some mutuals are acting weird toward me, like I committed some massive betrayal.

Here’s where I might be the asshole:
Yes, technically I could have waited an extra few minutes. But if I do that every time someone asks last minute, my plans never matter. This also isn’t the first time she’s done something like this she constantly assumes other people will bend their schedules to make her life easier, then plays the victim when they don’t.

I feel like I’m being punished for having boundaries.

So… AITA for saying no and leaving when I said I would?