Originally Posted by LostDragonflyWings
It sounds like you don't have a strong enough base to keep out of the saddle enough over the jump and to stay out of the way on landing. I would work a lot in the two point, at all gaits. Work without stirrups and work over trot poles too to help with your strength and balance. After you work on this, try approaching the jump in a two point and keeping it the whole way through. Also, make sure your stirrups are not too long. That could throw you off too if you lack the correct muscles.
I hope you heal up quick!
I definitely agree with all of the above! You didn't mention how often you are riding, that may have something to do with it too. If you're only riding a few times a week you may not be doing enough to strengthen those muscles to where they need to be for jumping. Which is where all the 2 point and no stirrups work comes in. 2 pointing the trot is very difficult and great for strengthening as well. Getting your base of support really solid is what will help you in the long run, although it is super hard to get there if you can only ride a few times a week.
I know some people's idea of a ride is to go plonk around for half an hour, do some walk, trot, canter, I never see them or the horse break a sweat. If you're not pushing yourself, you and your horse aren't going to get any fitter. For my rides, I like to have a plan, I do either no stirrups or 2 point in almost every single ride, and I make myself sweat! If I'm doing a flat school I'll do the first half with stirrups and the second half without. Or if I'm going for a hack out in the field I'll make a few rounds at the trot partway through and 2 point as much as I can. If you can throw down poles and do no stirrup and 2 point as you trot and canter over them, even better, it's great practice in balance and staying with the horse even if they sometimes take a bigger or smaller stride or an awkward step over the poles. Once that becomes second nature, cross rails will become far easier, since jumping is just a slightly larger canter stride.
I've heard that Pilates and Yoga are very beneficial for equestrians, since core strength is such a huge part of what we do.
So it may be partly fitness, partly just needing more actual miles and work in the saddle. It will come though! I'm feel very lucky that I was able to get into riding as a young kid, because it's kind of become second nature to me. I've tried to take up new hobbies/sports/instruments as an adult, and HOLY HECK is it so incredibly frustrating! I think it gets worse as we get older, I find myself just overthinking everything which only frustrates me more! Haha.
But stick with it!! It will pay off, I promise!!