They won't look at your high school grades. Just do well enough to get into a good college and to get the foundation knowledge you'll need to do well in that college.
I'm an anesthesia resident right now. I can tell you that you should do the best you can in high school and try to get into a good college. Once in college, play it smart. Don't try to be an overachiever and take 3 sciences and honors calculus your freshman year. Take it easy, mix up your classes to have hard and easy classes together. Keep up a 4.o and do well on the MCAT and you'll have a good chance at medical school.
BEWARE: if you take classes at a college while you are in high school, you will have to report those grades on your med school application! I wish I would have known that when I was in high school.