brum, I would be more concerned with demonstrating interest in and passion for your proposed major as well as strong letters of recommendation. The standardized tests, while important, are not make-or-break material. Pretty much everybody who applies to schools of that caliber have very high scores on standardized tests. Even so, the SAT tests are not suited to gauging the abilities of talented, intelligent, high-level students, and the colleges don't expect it to do so. I would contend that as long as your SAT scores are encompassed by or greater than the range published by the colleges, then the tests have zero bearing on the college's decision. Even if your scores aren't within that range, it's certainly not the end of the world. And if your scores are well above the range, you're not guaranteed admittance.
Similarly, most of the students that apply have similar acdemic records: lots of AP classes, a high GPA, and a very low class rank. Just remember that GPA and class rank are also not accurate reflections on interest and passion for science.
Just a little tangent that I find amusing: at my high school, there are 4 levels of honors pottery, so one can enroll in pottery and receive weighted credit for 4 years. In fact, the most difficult (in the sense of getting an A) class in our school (AP US History) is worth just as many rank points as honors pottery. There are also other classes that don't deserve weighted status but still have it (parenting and a class on how to use MS Word, anyone?). Essentially, at our school, you do not need to be an academic to have a low class rank.
Back on topic, GPA and class rank and AP classes are not necessarily related to one's major. There's an obsession with these kinds of things because it's thought that they're the key to getting into college. I've spoken with the admissions directors of Stanford, Harvey Mudd, and Caltech (quite extensively with Caltech's) and none of them have said that those were the kinds of things they're looking for. Their purpose is to demonstrate that the student can handle any work that will come their way--how much time you're willing to spend studying--not who would make a contribution to the field you're entering or who would represent the university well, which is the kind of student they're looking for. A more powerful demonstration of this is the order and quantity and quality of your science and math classes. If you're expected to take 4 science courses, 1 a year, but there are 5 at your school, take 2 in one year. If you're a year behind the highest level in math (i.e. there are 2 levels left but you only have 1 year to go), try to test out of one year and get into the highest class. If you're not expected to take a math or science class one year, take one anyway.
Also important are essays and letters of recommendation. These are the intangibles. A well-written essay can really raise the reviewers' opinion of the applicant (which, as I'm sure you can imagine, is quite important). In the letters of rec, specific events are important. Letters of rec. tend to suffer the same problem as school records: they're all the same, they all say "I think this is a great student." But why should the reviewers take one teacher's opinion over another? It'd be like writing an essay saying "I should get in because I'm a better candidate than everybody else" and not explaining why. Specific events support the opinion of the recommender and give the reviewers an opportunity to form their own opinion of you (an opinion that will stay with them more strongly than an opinion assumed from someone else) and set the letters apart.
Naturally, you should take all of this with a grain of salt. I'm not an admissions director--I'm only a student--but this is what's worked for me and (in the case of what not to do) what hasn't worked for my classmates.
cookiemonster