I remember first learning to canter, it was really daunting but now I love it.
I first cantered with an instructor running beside me but if you don't have access to a mad or fit perosn able to run with you, maybe try it out on a hack with a friend in front of you.
That way the friend and their horse will control the pace so you wont end up too fast, also it is easier to canter in straight lines if you are unbalanced.
Maybe you are not quite ready to canter yet, make sure you are completely comfortable in trot and see if you can up the tempo into a extended/running trot to get used to the speed and bouncing around a bit.
Remember to completely relax into the horse though when cantering but keep a firm seat to allow you to move with the horse.
Once you have got the balance issue sorted I would continue with it on the lunge to get used to the speed and somebody else can then control the horse.
Then add it into hacks or short sessions in the arena to build up your confidence.
I would also try cantering on a really good schoolmaster who will not attempt to speed up or get excited to get your confidence up.
Hope this helps and hasn't made yor eyes go fuzzy due to the large amount of writing