In the corner of the hall there was a small counter where the forms were to be signed, the teachers present there led the students to the counter one by one and the forms were signed by those who wanted to give the exam.
And it might seem strange to you but the majority of the students decided to take the exam despite the fact that they could lose their lives in the process. However, it was not even that strange if you looked at it from the perspective of this world.
Here all the students were sons and daughters of noble families, and to them reputation is a very big thing. Just think what would happen to the "reputation" of a family if their heir didn't participate in an exam in which all the sons and daughters of the other family's did, just because he was scared of losing his life.
Then there was the personal self-respect of the students; no one wanted to be marked as a coward. Hence most of them ended up taking the exam and signing the form.