Well, when I made good grades in high school, my main motivation was the scholarship money. I think you should definitely do extra curricular's and do a lot of volunteer work. This helps you get use to what you will be doing as a pre-med.
But, don't let your high school grades fool you from thinking you will be top notch in college. It is much different and you have to form much firmer study habits (when I say study habits, I mean that you should be as productive as you can for the limited amount of time you have to study in college).
In college, everything demands more of you. It is to make you more prepared for the real world. But, yeah, I don't see anything wrong with making good grades and having fun at the same time in high school. I personally thought high school was pretty relaxing compared to college (not to say that I took the easy path in high school at all, it was rather rigorous and I added on all the executive positions I had in clubs, extra curricular activities, volunteering, community college classes on the sides.... you get the point🙂).
Also, try landing a leadership position such as being president of student council. That always looks good on scholarship applications. Money money money. If you don't like to think about money, just think about how much happier you'd make your parents feel about you going to college!