I suppose the problem is now 70% of not balanced horse and 30% your aids. I'm telling you, you gonna laugh from this issue in 6-7 months, just keep riding. And ride sitting trot more, that will help you to stay more balanced if the horse speeds up in trot. And skip extended trot for a while...
Hi Jen,
I'd call my suggestion "back to basics".
After warmup put another rider on the horse and take it on lunge. Agree that he/she asks for canter and THEN immediately you ask canter the way you where used to when on lunge without rider.
Horse should get the point very quickly.
By the...