Don't be so hard on yourself!! I'm sure we've all done this at some point in our lives!!
First of all, relax, don't get high expectations, just start with a bit of flatwork, relax your wrists, let them droop slightly, think of fluffy unicorns!! Smiling always helps (me, personally) you to relax, and I have found that when I smile my hard hands disappear!! When you're jumping, sit nice and relaxed in the saddle, aim for the middle, if your horse refuses, don't tug him really hard in the mouth, growl at him if you must!! If you pull at your horses mouth a lot when jumping, he'll learn to fear it!
I'm no expert, but when in doubt ask someone experienced like a trainer/riding instructor, take your horse to a private lesson even someday and explain your problem, you'll be sorted in no time!!x