Problems with taking test. Help!?

Ok. I have this stupid math teacher who is teaching us to scale stuff like rooms and stuff from meter and such to a smaller measurement. Almost (including me) everyone in his class has a grade below a C. He surprised us by giving us a test tomorrow and if I don't get at least a B on this test I will haves failed his class. I'm really stressed out because the only thing that counts in his class is tests and if you miss like 5 he says u failed that test. I'm only in middle school! Basically I haves failed his tests in the past which left me with a lack of confident with I take quizes/tests. So every time he gives us a test I get really stressed out over it and spend hours studying for it and still fail. I need some advice on how to get through the rest if the school year without going nuts over this. Can anyone help me here with my lack of confident? Before I got him as a math teacher I have gotten almost A's in everything now I have mostly B's and a couple A's. Please help! Srry for misspellings and stuff I wrote this on my phone.