It's riding weather now. I suggest that you ride only at the walk, starting tomorrow, for one full hour every day for a week. You want to teach your body how to feel weighted. Sitting the trot will just throw off your balance. The walk is the best way to teach you to both relax and to move with the horse. After a week, you should be able to play with the posting trot--post, post, sit...sit, sit, post--make a game and exercise with it. Your canter seat will also improve.