AITA for eating my girlfriend's pint of Ben & Jerry's?

My GF (28F) bought this super expensive pint of artisanal salted caramel ice cream because she had a really rough week at work. She was looking forward to it all day. I, being hungry after the gym, saw the pint in the freezer. It looked amazing. I ate the whole thing.

She came home, saw the empty pint, and was clearly disappointed. She said she was really looking forward to it and now she doesn't have it. I said I'd buy her another one, but she's still a little bummed. Did I mess up? AITA? It was her ice cream, but I was really hungry!