I think that the best thing you can do, is to remember that you_are_in_high_school. . . It's going to be okay, even if you are not a great studious high school student.
I was a COMPLETE under-achiever from 10th grade on. I'd been raised in excellent Catholic schools, then I started public school, which didn't challenge me a bit. So I never studied, didn't get one of the pointless special high school diplomas, skipped a lot of classes. You're going to get to college (assuming you don't fail your classes), and then you'll see that high school is not at all relevant to reaching med school.
But the faster you learn to study, the better. The big moment for me (later in college, unfortunately) was when I learned to study immediately (EDIT: as in promptly and on schedule, and "study" means "read some") and never get behind: it's not easy to stay disciplined, but that undoes all of the stress I ever feel about school, thus making it easier to learn and retain the information. A tip that is completely relevant to college, is to make sure you are happy and taking care of yourself: if you're depressed or angsty (angst was my favorite part of years 13-17), you'll have a hard time studying. At a certain point--for me it was around 22, so don't be like me--you'll get to the point where you'll actually look forward to studying. It's not straight-forwardly helpful, but I just wanted to say, in a couple of years, you'll see how little high school matters in any way at all. So hopefully, knowing that, you'll be able to chill-lax a bit, which should help with being able to sit down and study. Stressing about procrastination is not helpful.