Nervous Breakdown before a Test

Today, I was so nervous for my interview and I forgot a lot of things that I should have said to promote myself. I need to get myself calmer somehow or I should get more practice. After that, I had a quiz from accounting. I had filled in the first answer right but after that, I felt that I was wrong and had changed it. When I finished the test, I was like the last person done. I went to check the textbook and I found out that it was wrong. What a bummer, I need to find a way to remember the topics well.