First off, calm down and carry on. In high school, major in (take four years of) English, science, and math. If they offer calculus, grab it; if not, take it soonest in college. Do not neglect English. At the end of everything, it will be your bread and butter.
When you're close to graduating from high school, you will apply to colleges. At that time, you and your parents will negotiate with colleges how much all of you will pay. In college, tell your adviser that you want to major in biology or chemistry, all the while fulfilling the requirements to apply to med school. Not every one gets into med school. You want to have an option to apply to graduate school in chemistry or biology. There are no jobs for graduates of "premed."
Once accepted to med school, you will do a rotation among departments. One of them will be oncology. You can see how you like it. It will be triumph and tragedy. You will lose many patients whom you knew. Once you graduate with an MD, you will do a residency (four years?) in oncology.