The only reason people stress out with VCE and life in general is because they take a bleak view.
What you have to remember is that it's not the end of the world if you don't get into the course you want to get into now, there are plenty of ways to get there later. Not only that, but there are heaps of careers which you might be interested in as well, have a look at those - you might be satisfied working in those fields. You need to find ways in order to fully insure yourself against anything that can happen in VCE. It's just like driving a car, once you have insurance, you feel safer and more confident on the road - less nervous.
In order to do well, you need to separate yourself from what you want. Instead of seeing VCE as a giant monster and roadblock to where you want to go, you have to see it as a game - as a sport - where you are challenging and pushing yourself to the limit, to push yourself further than what you've been able to achieve before, and then push one more step beyond that. The more you see it as a roadblock, the more you will approach VCE defensively.
For me, I always saw VCE as a challenge to do as well as I could for the fun of it, to prove myself, for my own pride and to just show myself that I'm really up there with the best. That's because even though I wanted to do Medicine, I had other backup options. I knew that I would do a Bachelor of Science and then try for graduate entry, if not then I'll do Education and become a teacher after that, a career which I am more than content with having. Thus, having myself fully insured, I just went into VCE having fun and doing for the challenge, like an athlete trying to beat his personal best.