I signed up for minecraft at school with my moms email and she got alerted what do i do she got mad and said i'm playing games at school?

Your school offers minecraft as a course… So awesome

It depends. If the school allowing you to sign up for Minecraft as part of a class or activity, then you should explain this to your mom. She would then have to complain to the school's administration instead of you. If you were just playing it for fun though, you should probably apologize and ask for her permission before playing again.

Your mother's reaction is PERFECTLY JUSTIFIED as you're doing something that you probably SHOULDN'T be doing at school.

If your school is utilizing Minecraft as part of a class, they would be running the Educational Edition that wouldn't require any outside registration. If it was a one-off deal, the school would generally send a consent form regarding it BEFORE the account was created.

In short, just apologize to your mother & you might have to suck up to her for a while (doing extra chores & errands) for this error in your judgement.