20 kids is a nice small class, yeah..
maybe focus on any friendly eyes/faces of friends or such, or just look around the room randomly.. knowing your subject well is good, yeah...
maybe practise at home a bit.. there were threads on giving presentations here before, with some tips..
it's not nice to say a girl is a b**** (even if she is, sort of..) maybe she was just having PMS?
Working in groups can be tricky.. (or fun) It's probably easier if people who wrote it presented it, as they may know more about the subject matter, on the other hand it's good if everyone contributes a bit..
I've been in groups where only a few did the work and it wasn't good, much better if everyone does something.. It's better to agree on roles together though, ideally at the beginning.. If you'd feel more comfortable writing/preparing stuff, you could offer to do it then..
It's your decision how much to talk, if you have interesting things to tell, and do it well, it might increase your grades or popularity with the teacher.. (and maybe even with classmates if you do it well..)
For some people it works to try to stutter on purpose (they can't then) maybe try and practise it at home?