Am I the Asshole?

The original post: /r/amitheasshole by /u/-TheWillowTree- on 2025-04-06 00:30:13.

So like the title says I (19f) was left at home while my sister (30f) and her kid (7f) went to a family reunion we were all supposed to go to. I had been told we were leaving at 5 after my sister got off work. I had all of my things with me and ready to go by 3 as I know she occasionally gets off early. At 3:30 she had gotten off early and called for her kid and I just assumed she was getting her ready as I was in the bathroom and she had specifically only called for her daughter. When I got out of the bathroom everyone had already gone and I was left alone in a house with no food. I called my sister and asked if they had seriously just left and she told me yes because she told me to be ready by the time she was home. I got kind of upset at her implication me peeing was being unprepared and I raised my voice at her for leaving without even checking if I was actually ready so AITA?