Baby girl, you ain't gonna go blind, who told you that lie?! First of all, stressing out like that isn't good for ANY part of your body. For serious! Just relax a little bit, I know you're going to be okay.
Second of all, you should know that 5.5 isn't the end of the world. If you're too young for a laser operation then you must be in your teens. When I was your age, I had a similar prescription, maybe mines was like 5.0 back then. But still. I'm -6.5 now and in my 20's. It WILL get worse but not that much worse though. You definitely wont go blind from your bad prescription. I would say contacts probably do go to about -10 or -12 or maybe even to -14, but I'm not totally sure.
And the best advice any of us can give you is to DEFINITELY go talk to your doctor. Hearing advice from a trusted professional will obviously make you feel safer, right? And eye doctor trips are fairly cheap and easy to do so you shouldn't have a problem talking to a real doctor instead of us.
However, I do know some things you can do to improve your eyesight, or at least stop it from getting worse, but you have to be dedicated (and that can be hard as a teenager to stick with things like these but it's up to you).
You could take the pills. There are pills designed to keep your eyes from getting worse. I was taking this one for a while, it's called Bausch and Lomb Ocuvite PreserVision. You have to take like four pills a day, and they're HUGE pills. But the pills have things like Vitamin A (beta carotene), Vitamin C (absorbic acid), Vitamin E, Zinc, and Copper. Actually, those are the only ingredients. So maybe if you just ate foods that had high levels of those vitamins, like carrots.
Also, taking your contacts out at night EVERY NIGHT and using Clear Care Lens Solution is a good idea. You have to make sure you don't do any damage to your eyes that will prevent you from getting Lasik in the future.
Also, there's the See Clearly method. They are eye exercises. I know a girl that did them and she had really good results but her prescription was very low to begin with so I don't know how well that will work for people with higher prescriptions.
The main thing I can tell you is to please don't stress (that makes it worse!) and to see your doctor! I gauruntee you'll be okay.