First, let’s pull up the latest Common Data Sets for Cornell, Dartmouth and Caltech.You should do this for the other schools on your list as well to see how your objective stat’s stack up. http://irp.dpb.cornell.edu/wp-content/uploads/2018/03/CDS_2017-2018.pdf; http://www.dartmouth.edu/~oir/pdfs/cds_2017-2018.pdf; http://finance.caltech.edu/documents/479-cds2017.pdf
Parsing through the info you shared:
GPA/Rank. You say your rank is around the top 10%. Do you have an idea if you are closer to the top 10% or the top 5%? If we look at Cornell, 86% of the matriculated students were in the top 10%, 93% for Dartmouth and 97% for Caltech. For Cornell, this data includes all undergrad colleges, but I suspect the College of Arts and Sciences, which is what you would likely choose as a premed, has higher stats as a subgroup (also for test scores). For Cornell and Dartmouth, also remember there are about 200 recruited athletes, many of whom will have lower stats.
Courses taken. Colleges do look at overall course rigor, including senior year classes. Will your counselor note that you have taken the most rigorous courses offered? I know there has been some back and forth on Calculus AB vs BC, and if Stats is your only option so be it, but you would be seriously at a disadvantage if Calc is not fresh in your mind and you are a STEM major. I’d suggest taking a summer refresher course or work with a private tutor before heading into college.
Test scores. With a 32 ACT you are just above the 25th percentile for Cornell and Dartmouth (but note my comments on athletic recruits and Cornell College of Arts and Sciences) and well below for the 25th percentile for Caltech. Do you have SAT2 scores yet? They will be required or at least recommended for most of the highly selective schools.
EC’s. The top schools admit both “round” and “spikey” kids. I disagree with the posts that say your EC’s need to be consistent with your intended major. I do agree that what matters for EC’s is depth and quality of participation and achievements, not the length of the list. The successful candidates present a consistent story about themselves through their classes, LoR’s, essays and EC’s that portrays someone who will make the most of the institution at hand and who will be a contributor to that community.
Finally, the list you presented are of some very different schools. The only common thread is that they are highly selective. Cornell is huge and rural. Dartmouth is small and rural. Caltech is frankly for science geniuses. UC is in a major urban center. They all have different emphasis and campus culture. Do you fit these schools and vice versa are critical questions.
Bottom line, your current stat’s put you in the ball game, except for Caltech IMO, I’d definitely try to get the test scores up. But more importantly, if you want to take a “shot”, shoot at schools that fit you and vice versa.