Originally Posted by ShaneBaybutt
Shorten the stirrups up so you can balance more when you are doing the canter then work to taking the stirrups away and canter this will help your position and balance then gradually work from high to low in the canter or ask some one to lunge you or you could possible use spurs to aid with the transition.
The horse in question is young and green by the sounds of the original post.
If this is the case, I wouldn't be removing stirrups completely - that's great for rider position -> on an established horse. NOT on a green horse.
The OP also said that their heel comes up and they lose balance - spurs? BAD idea.