Don't stress! It's not like the teacher can just take the test out of your hands and say "nope! you can't finish this graded test!". Also... eat a good and healthy breakfast. Just remember what you studied! If you can do it on the white board, you can do it on paper! :)
First, (this optional, but helpful) very once in a while, change your studying environment. Then, when taking the test, you'll remember that you learned something somewhere (Kind of new places are more useful, like on the roof. Don't choose dangerous places :D and do not do this excessively, because it will make unable to study in a certain place) Second, at the time of taking the test, you may feel that you don't remember any thing. This is because you wanna remember everything all at once. Impossible! Try this: now, say as many words as you know! You will stop somewhere, but you know that you CAN speak. So, just relax, read all the questions once, and then start answering them (If you do not remember the answer of a question, after a little while of thinking, leave it, you'll soon recall it) Good luck!
Begin studying a week or two before. Go over all your notes and homework assignments. If you get stuck on any particular things focus more attention on them until you get them sorted out. Don't cram the night before. It's counter-productive. A good restful night's sleep will do you much more good. Eat a big nutritious breakfast in the morning before you leave to take the test. It will help with your ability to focus. During the test stay calm and confident. You've done your studying and know the material so no worries. Good luck.
Go to the bathroom first if u can go run around the school sit down deep breaths ignore the world that's around you until u hear what your SUPPOST to and consatrate on the test and are you taking the MCAs