When I first started I did the same thing. You need to flip first and then rotate. If you leave the wake while twisting you will land on your butt. No one ever told me that - if they had, my butt would look 10 years younger right now. Anyway, try leaving the wake like you were going to a front roll and wait till your 1/2 way to let the board go 180. It's all about how you leave the wake (all inverts are like that - in my opinion). Rip it brah.
Oh yeah, don't pull your legs in, it won't help much but taking off correctly will. If you know how to do a tantrum you should be able to learn it pretty quickly.