When I was a kid, the horse I was riding in my second-ever riding lesson started cantering, and I fell off. After that I was terrified to learn to canter for a long time. So I understand.
My only suggestion is to take your time. If cantering is scaring you, why not back up a bit and work on trotting? Work on exercises such as trotting without stirrups, trotting in your two-point, relaxing your seat at a sitting trot, trotting bareback, going over trot poles, etc. All of these things will help your balance (and hopefully confidence!), which will subsequently help you when you do start cantering.
When it's time to attempt a canter again, make sure you're on a lunge line. Even though that scares you, I'm assuming it scares you less than cantering on your own, right? Your nerves might be getting the better of you at first, but once your horse does pick up that canter, I think you'll find you're able to relax. Just remember to sit up nice and tall and keep weight in your stirrups so you don't lose them.
Good luck! And don't forget to check your girth before you ride. :) I often find I need to tighten it a hole between the barn and the arena.