How do I talk to my teacher

In summary, I got a detention for PE because I 'asked' someone to switch classes with me. The lesson was to decide which class to sort people into. Now, I got the detention before they signed my name off on any class. So I don't know what class I'm meant to be in and I don't know how to go and ask my PE teacher which class I'm in because I'm scared she's going to go on a rant. My main worry is that I'm going to start crying (again) because she terrifies me.