SOMEONE HELP ME PLEASE!

I’ll keep it short:

I’m 15, and my mum takes my phone at 10pm on school nights. Weird, i know. Tonight, when she was asleep, I snuck into her room, unplugged my phone which she put on charge, and took it. That was 2 hours ago, it’s now 4am. Her alarm goes off between 6:30-7am. I can hear that she just turned over, so she isn’t asleep, which means I can’t put my phone back. When she wakes up in the morning and sees my phone isn’t there, she’s gonna freak.

I also have a maths assessment tomorrow morning, so im already screwed. But has anyone got any other ideas than waiting on my phone until she might be asleep, then trying to put it back?