Do you really have to be a genius to get into an ivy league?

I'm only in ninth grade but college is all i can think of. I am in all honors cles and am in 3 maths ahead of my grade. I will also be attending a few cles at Eastern Virginia Medical School in the fall. I have been playing the cello for 6 years and i am 6th chair in an acclaimed youth symphony orchestra. I play three sports and have a bright future in all of them. My dream is to go to Dartmouth and become a neurosurgeon. It is all ive been thinking about since i was young. So my real question is what are my chances of getting in and if I get a few B's hearand there will that really hurt me?