I agree with kayty.
Use rhe school exercises to help you bring the canter back to you. perhaps don't canter willynilly around the school.
Work on a 20m circle spiralling in and leg yielding out in trot. at a given point as you return to the 20m circle, pick up canter. spiral in and trot. repear ad nauseum on both reins.
What is your canter like on the lunge? If it is ok, perhaps it is an issue of balance with rider as well. try double lungelines and doing the same exercise fron the ground. Transitioning in the same spot works well as well.