Looking good for just starting out; I can remember when I did.. it was bad. LOL.
1.) Shorten your stirrups a whole or two so you can get off your horse's back a little easier, and so you can have your heels down.
2.) Move your hands more towards the middle of your horse's neck, grab mane if you need to in the beginning, so you won't be on his mouth as much. If your horse takes off after the jump move them about a quarter way to the middle so he has just enough release, but not enough that you can't control him.
You can practice your jumping position on the flat too. That's what my instructor made me do so it got stuck in my brain; also helps with heels down.