The MCAT is a fvcking scary test.
With that out of the way, there are a number of ways to deal with it. I taught Kaplan MCAT prep classes for about 3 years, so I'm well aware of the stress that people face. A couple of bits of advice:
1. Relax.
2. Relax.
3. Relax.
4. Remember, you have studied all summer. Also remember that you've taken classes in those subjects before. You know the stuff....trust me you know the stuff.
5. The most difficult part of the test is application of the stuff you know. Try to remember...the test is testing critical thinking, NOT memorization and recall of facts. So, you get a passage, you read it, and look at the questions. Try to figure out what abstract idea the question is trying to get you to think about. Just try to sit back and think about it; remembering that most likely you've never seen the passage contents before. But you have 2 things that the test makers are testing....a) a baseline level of science knowledge, and b) critical thinking ability.
5. continued...So, you face a passage you know nothing about...then you get a question which you know even less about. Don't panic. Read the question while you cover up the answer choices. Think about what the question is asking. What part of the passage are they referring too. Try to answer the question (very generally). Look at the answer choices and see if you find something that make sense with your answer. Also, eliminate answers that are unreasonable. Remember, the test makers DO NOT EXPECT you to know the contents of the passage before hand; thus extensive knowledge of science will not help you in this regard (it will help you think better though). So, think about what is being asked, eliminate answers that you realize are unreasonable given your knowledge of science and what was given in the passage (and common sense), and you should have it narrowed down to some pretty reasonable choices. It's really that simple. Now I know that its a bit late to change your entire thinking process, but again, simply approaching each question like that may help.
Given that the test is on saturday...here's what I'd do. Rest of today...study some high-yield type facts, flash cards, or whatever. Thursday: do one entire practice test and go over the questions, perfecting speed and timing, and going over any questions on which you've made fundamental mistakes...but don't get caught up in small details. Friday AM: take ONE practice section. Chill. Friday PM: take another practice section. Chill. Get all of your stuff ready. Whatever you need. Magic rub eraser (best eraser period for test forms), get your lunch (or lunch plans) ready, get the location and parking scoped out, and chill again. Watch a movie, whatever. Go to sleep early if possible (also do that the next couple of days, getting up at test time). Get to the test center 10 mins before they say, otherwise you'll be really nervous for no reason.
If you go in with the right attitute, you'll do fine on the test. Again, trust me...i've seen lots of people go in with a good attitude, after a summer of hard work, and do fine on the test. So, I think you can to.
PM me if you have any more questions!
Good luck...you'll do fine.
MD.
BTW: the SAT/ACT are useless, virtually meaningless tests. With grad school tests like the GRE, MCAT, LSAT, you can't take them as often, schools usually look at all results, and things are competitive on a much higher level (remember, they are standardized, and thus, bell-shaped....also remember that fewer dumb fvcks take those tests vs. the SAT, thus making the test much harder to do well on).