I'm writing this from school
What happened why are you chatting from school?
Can't get inside my apartment.
Well, if the school is okay with you being there, then it is fine. Better than standing out in the cold. Next time, you should have a spare key nearby to prevent this from happening again.
Why don't I just break a window?
If you break your window, you will be damaging property that will be costly for you to repair. If you need to gain access back to your apartment, you should involve the landlord if they have any spare keys so that you don't damage something you will regret later.