AITA for saying my 13 year old cousin can watch herself for one hour on a weekday.

I was visiting my cousin who lives in a different state. I hadn’t been to visit in a while so they were really happy to see me. My cousin has a 13 year old daughter. I was told that when I visit I have to take care of my cousin’s daughter and make sure she gets home from school. I explained that I’m off work to visit and didn’t think it would be a big deal to take care of her til my cousin came home an hour later. I was told that I was being lazy and I need to take my responsibility seriously. I got a lot of blame and don’t think it’s fair.