I think "pressure" (壓力) may be a better word choice than "tension" (張力).

Tension will make us make Mistakes

We have practised trial teaching in the afternoon. Some girls was were so nervous that they made a bit of few mistakes in class. Some of them greeted for us:“Good morning, boys and girls." at the beginning of a the class. Also, some students made mistakes. For example, a girl answered the teacher's question (by saying) : "I am going to be an actor. " and another girl said“ I am going to be an engineer” and so on. So Too much tension will cause [lead] us to make mistakes. But how What can we do to avoid the tension？ Maybe we are just be lacking in of confidence.

tension will make us make mistakes

We have practiced trial teaching in the afternoon. Some girls were so nervous that they made some mistakes in class. Some of them greeted us “Good morning, boys and girls." at the beginning of a class. Also, some students  made mistakes. For example, a girl answered the teacher's question "I am going to be an actor. " and another girl said“ I am going to be a engineer” and so on. So too much tension will lead us to make mistakes. But what  can we do to avoid the tension？Maybe we just lack confidence.

You should not be afraid to make mistakes,it is part of the normal learning process.In fact we learn by making mistakes.