Wow... That is so irresponsible of your teacher!
At the school I just graduated from, they said that if you were pregnant you couldn't attend gym class, because they couldn't guarantee that what was done wouldn't hurt the baby or you...
Of course this was denmark... And I don't know how it is where you are, I don't even know how it would be in the other end of my country!
Gosh... If I was you i'd simply refuse. I mean are they even aware what consequenses it would have for the school if you got hurt in any way?
I'm sorry, but hearing that makes me angry. I know exercising is good for you when pregnant, but there has got to be limits. I hope she isn't pushing you into stuff???