I love that you're looking forwards and are alert. Roll your shoulders back and open up your chest - keep in mind this action will make you want to hollow your back so you have to tighten through the core. Think of sucking your belly button to your spine with your abs. It's hard to tell with the mane in the way, but I'm willing to bet you're breaking at the wrist - make sure your wrists are straight, thumbs on top. It may help to think of your thumbs keeping the reins from slipping, rather than your ring finger.
Your heels are down but they're forced and you have the contact on the back of your calf. My guess is you're thinking "heels down" and jamming them down and rotating your toe to achieve contact. A bit of rotation out is fine, even necessary, but you don't want your toes to be pointing east and west of your horse though! Think of wrapping your lower leg around and down, and try to touch your heels together through your horse. Your legs are your base of support.
IMO you don't need to be as far out of your tack as you are over a jump this size. Posted via Mobile Device