For many, those first four or five canter strides are tough - especially if your hose tends to blast into a canter, or is a bit jerky. Think and feel it next time - are you trying to grip with your knees or thighs? That will squeeze you up and out. My old TB tended to have a beautiful transition, then would steamroll ... gain speed, get all excited and we were off!!! I would always tend to get stiff and bouncy as I anticipated having no control.
Do you have any leather lined Jods? You can pick some up at places like Country supply rather cheaply. Sometime that extra grip gives tons of confidence.
It is very important to "feel" your horses strides and move you hips a bit - much like anticipating a wave when you are standing on a boat. If you try to remain ridgid, you will be bounced.
Even when you are upright, prim and proper, in perfect English equation position, you must think of yourself as fluid - almost like a slinky, from bellybutton to butt. That is your shock absorber, and is constantly moving and adjusting.
"There ain't no vaccine for stupidity* Maxine