I think you should shorten your reins a good 4". You don't have much contact with your horses mouth and your elbows are set too far back (it looks as if you're pulling back, but still with no contact?). Also, try to focus on keeping your thumbs facing up.
Your toes should be pointing straight forward, not out to the sides and it looks like your stirrups are too far back towards the arch of your foot. The balls of your feet should be what's resting in the stirrups.
It also looks like maybe you're pinching with your knees a bit? It's hard to tell but you look a little stiff in your lower back and hip, which can be caused by pinching at the knee.
That being said, I really like that you seem focused, with your head up and looking at where you're going. Your horse is lovely. He looks very relaxed and content to be working. Both you and he are turned out very well for a schooling show and seem to be a great match!
Thanks for sharing your pictures :)