Hey, man. You're going to make it. I promise you. If there's one thing I know about chronic worriers, we always get things done. It's just what will your quality of life be in the mean time?
Though i'm in an entirely different phase of life, I understand what you're going through. I'm just beginning a doctoral program in music, and have to give a recital in november, and perform a big role in the spring opera. I battle with myself on a daily basis, and spend a lot of time feeling overwhelmed and being afraid i'm going to fail and not accomplish my goals. Here's what I do to tell myself i'm going to make it.
1) step away from the big picture. The big picture is the problem -- that's what's intimidating. Know that little steps toward that goal, even when they don't feel like much, will bring you closer to it.
2) if you're like me, you end up doing a lot of things at the last minute. Tell yourself that's ok. But every little thing you do today will reduce that last-minute push and make you feel better about it.
3) focus on the process, not the product. Enjoy the process. As a fellow artist, I can tell you that art is about creation, not about the goal. If you focus on the goal, you will only be disappointed in the end, because you've worried your way through the best part -- the making of the art! I sang a role last fall, but was so caught up in "getting it right" during the rehearsal process that I didn't enjoy the performance when it came time. It was a relief to be done, rather than a fulfillment.
4) set small goals for yourself every day. I know that kind of goes against my last point, but you will have less things looming over your head in the long run.
5) give yourself permission to have a bad day. Every so often, you will feel overwhelmed by things. It's inevitable, and you really can't prevent it. Go easy on yourself when that happens, and don't feel guilty for it. Take it as a sign that you need to do something nice for yourself. For me, those are the days when I crash out on the couch, watch star trek, take a bath, and eat lots of ice cream!
6) give yourself permission to have fun! You're a senior, and this is your year! Enjoy it. Again, do things you enjoy. Hang out with your friends, do things you like, and be unashamed about it.
7) talk to people who understand. People who tell you, "just relax" do not understand. People who will help you become the person you want to be do. Find a teacher or counselor, a friend of sibling, a clergy member or psychologist who you can be honest with, and whose advice you respect. This does not make you weak. It makes you strong!

say "what the hell!" at least ten times a day, and remind yourself if something is worth doing, it's worth doing half-assed. I can say that because i'm a fellow perfectionist. Things are only overwhelming when there's a need to make them perfect. Take away the need for perfection, and you've taken away a lot of the stress.
9) be committed to change within yourself. What you're asking will require you to change the way you look at the world. That process is only beginning, and will only continue as you go on to college or whatever your next phase of life is. But it is worth doing, and I applaud you for it!
10) feel free to say "no" to things that get in your way of becoming the wonderful creative genius that you want to become. Taking too many classes? Drop one! Have too many projects? Find a way to make some of them simpler! You've got a lifetime ahead of you -- you don't have to do it all now.
I think ten things are good enough for now. I could go on, but i've got my own daily goals to accomplish. And a bowl of godiva ice cream with my name on it

thanks for giving me a forum to write, too. It helps me stay "honest" to the person I hope to become. Know you are in my thoughts and prayers, and I wish you nothing but the best.
Peace and blessings,
paul
btw, my last job was as an academic advisor at a large public university. So even if you think this may run contrary to your goals in school, I guarantee you it will help you!