You're probably opening early because you can't see the landing (unless you take it really big
). It's normal. Next time it feels good in the air, keep your shoulders moving forward over the board at the end of the trick. Don't try to fully over rotate it, as that may end in disaster. I scorpioned pretty bad a long time ago when I took it too far.
I agree with others though, edge hard, chest up off the wake, then duck your head and shoulders to get the rotation going.