I can totally sympathise with you! Every year before recurrents i get that same feeling, even though i know i know my stuff, upside down, inside out and back to front!
I dont know the airlines proceedure but at the start of the training i would mention to your trainers that you get very nervous in exams. Certainly all the trainers i have worked with will help you in any way possible. Be that through extra tuition or just the 'heads up' on when the exams will be and what they will contain, in order for you to feel more confident.
A good idea is to 'buddy' up with someone for your study sessions. I find that you learn almost as much asking questions as you do answering them rather than staring into an SEP manual for hours on end with no interaction with anyone.
During the course ask as many questions as you need to....remember 'there is no such thing as a stupid question' if its going to help your understanding of a topic.
Finally as Virginia quite rightly said, you sound like you are a great cabin crew member. Think positive, be confident in your abilites and have fun, stressing will not help you at all.
Good luck and safe flying.