Talk to the teacher about this. I'm a teacher and I have signals for two students who have this fear. For one, I give a finger signal which means I will call on him after this student, and for the other, I call on her first. Then it's over. This makes it easier on them, they seem more relaxed now, and nobody else notices the signals.
Be prepared and don't be afraid...you have a 50/50 chance--either you will be right or you won't. You are probably right. I used to be afraid to answer and then when someone else gave the answer, that was the answer I was thinking. Also if you answer wrong, someone else will probably have been thinking the same as you and the teacher, if she's / he's a good one, will clear it up for you and the others who didn't understand.