Now I know why premeds are the least liked majors in college. I was a physics major as a premed, and whenever I told someone I wanted to get into medical school they always looked at me like I wore diapers and bitched about getting an A-.
Which I did do from time to time, not the diapers thing but the A-.
To swissmed, it's good that you're taking initiative early on, I would recommend using SDN mainly as a resource to figuring out how to shadow and what volunteering you should be doing. Realize that college level courses are a lot more competitive than high school courses, in my case there was really no comparison. It of course depends on your major, I suppose majoring in biology isn't going to be as rigorous as say electrical engineering, but they all have their unique complexities.
You need to approach life maturely, realize that there is a lot of hard work involved with success, and don't act like you've accomplished anything even when you have. It was Gandhi who said that everything you do is unimportant, but it is important that you do it.