AITA for refusing to leave college because my mom needed me as a babysitter?

Bassically, I have a little sister (9 years old) who I have always been on really good terms with. I was essentially like her second mom- even FIRST mom, since our mom was always busy with work.

We like to watch movies and sometimes I even play dolls with her. Essentially she sees me as a cool babysitter not a sister 🥹

She's quite spoiled, but she knows how to get her way around things. Like there's a reason everyone spoils her so much! 🙃

She's my mums favourite child. I've never really been bothered with it because as a younger sibling, of course she should get more attention.

I'm starting college, and a few days in, I get a call from my mom demanding I come home immidietly. Apparently, my little sister had been sleeping on my bed crying for me to come back home for days and whining to my parents.

My mum demands I take atleast a week of a break to properly end things off with my sister. I'm coming home every 3 weeks. It's not like I'm leaving forever.

I refuse and she calls me an asshole for not wanting to see my poor little sister.

I tell her that I literally have school that I paid for and I can't constantly look after his. I told her to emotionally support her herself and I shouldn't have to do absolutely EVERYTHING.

Anyways reddit, AITA?