Firstly, I’d lengthen your stirrups a hole or two - they look a bit too short. I’ve ridden a few slab sided horses that I preferred this length of stirrup on, even over tiny fences, but it looks like it’s hindering you more than it’s helping.
Use the arrow keys to go frame by frame of the video, particularly at takeoff of the jump. In an ideal world, you should be able to take the horse out from underneath you and you’d be able to land on your feet. As you can see, you would probably land on your nose. This is happening in part because you throw yourself up her neck in anticipation, and also because it looks like you’re lacking strength, which is causing you to pivot around the horse (heels go back, head goes forward, and vice versa towards the landing). On the landing, your balance is too far forward, but you don’t have enough strength to gracefully dampen impact through your legs, and so you collapse forward onto the neck.
There are all kinds of exercises you can do to improve your strength on the flat:
On the flat, ride in two point at w/t/c, both directions. You should be able to make it around the ring without having to sit down/grab mane/etc.
Post at a walk - you don’t have the horse to help you.
Ride without stirrups for a few minutes every ride.
Set up 4 poles about 2 trot steps apart (~8ft, depending on your horse’s stride) and trot over them in two point. When that’s easy, start slowly lowering down into a deep two point as you go across each pole - the first one will be normal two point, then slightly lower, and lower and lower, sending your hips BACK until you’re as deep as you can go without actually sitting in the tack. Come around and do it in reverse - start deep, then raise up over each pole until you’re in normal two point at the end. You can repeat this with canter bounce poles too.
Post the trot to different variations - sitting two (up-down-down-up-down-down), rising two (up-up-down-up-up-down), or sitting/rising every 3rd step (up-down-up-up-down-up-down-down). You can even do this at a walk while you’re warming up.
If you’re only riding once or twice/week, you can also do basic exercises at home to build strength. I’ve also found (and bear with me, I know it sounds crazy) walking with bent knees while focusing on keeping your upper body totally still and at the same height is a good exercise for body awareness. Try going up stairs, walk quickly, walk slowly, try to deepen your squat position, step up on a box while keeping your upper body at the same starting height, widen your stance so you have to shift your weight from left to right as you walk, etc. The goal isn’t necessarily strength building, but it will really help draw your attention to how your legs must move independently from each other and your torso, but also maintain strength/balance through a wide range of motion.
