If possible, I would recommend that you take any other classes that the college has to offer and try to see if you can assist any professor or graduate student in their research that interests you.

If your college does not offer for instance biology classes, you may want to find somewhere in the area where you can volunteer or get an internship while attending school so that you can gain some experience in biology or any field that interests you. Good places to look for these would be at a zoo, wildlife sanctuary, or some biology related non-profit, in case that biology is your interest.

Not all biologists received a biology degree as an undergraduate; many people change focuses throughout their career so I think you can still become a biologist at any time of your life. You just need to gain some experience and then possibly acquire a graduate degree in a biological field. The same applies to any other field that interests you.

Yes, you can - but I will tell you that commerce is a very different field than the sciences. You'll have to choose while in college which classes you're going to take. I notice that you're eleventh grade, which means that you haven't started college yet, so you still have plenty of time to choose.