Really cute horse! I like your seat at the canter, it seems really secure and you're moving with the horses motion. If I were you, when I do my jumping courses, I would shorten up my stirrups probably 2-3 holes. Your position over jumps isn't bad, but you need to get your heels down, and it's probably a lot harder to do with really long stirrups. In some of the photos you posted, it looks like you're in a chair seat. Your toes should be underneath your knees, you shouldn't be able to see your toes while you're riding.
I would also move your stirrups closer to your toes(like the balls of your feet) rather than having them so close to your ankles. It'll help get your heels down and your legs underneath you.
When you go over jumps/obstacles, you should also grab some of your horses mane. It'll help you maintain balance over jumps and you won't pull on the horse's mouth in the process. C: