I get anxious if I am reading something and others finish before me. Doesn't matter if they are quiet. I know they are done and I'm not.

And then there is the time pressure. Even though I have enough time, but because it is there sometimes adds to it.

And the need to get a perfect mark...

I remember being nervous doing my learners written test and the person read each question to me as I did the test and that helped.

ah the joys of life.

Talk to the teacher, maybe they can have you do it in another room, in the back of the room - somewhere that you have more space, give you more time, depends on what causes your anxiety.

Finally, you just have to tell yourself "do your best and that's all you can do". (blah blah my best isn't good enough? blah blah... pretend a friend or parent is telling you this, or you are giving this advice to a friend.)