AITA for giving away the concert ticket I'd promised to hold until Friday evening?

I handed Mia the spare concert ticket at lunchtime on Friday. At six that evening, my friend Aaron texted, "Shift swapped. I'm in."

I'd told Aaron on Monday that I would hold the ticket until seven on Friday. He couldn't confirm before he knew his work rota. The tickets were $68 each, and I had paid for both.

On Thursday he still said "probably." Mia then asked if I had anyone for the spare. She could pay immediately and wanted to know by Friday lunchtime so she could arrange her own weekend. I said yes to her because I didn't want to reach seven with a ticket and no definite companion.

I didn't tell Aaron before handing it over. When he confirmed, I replied that Mia had already bought it. He sent back a copy of my Monday message and said he'd spent the afternoon arranging the shift swap on the understanding that he still had time.

I offered to ask Mia whether she'd let him have it. Aaron said he didn't want to take away a plan she'd now made too.

My reason was avoiding uncertainty, but I had given someone a very definite deadline and then acted before it. AITA for taking the sure offer?