Sounds like you're doing what's necessary to initiate a backside to frontside turn, but you may not be leaning forward enough when you make the transition. For most people who are still new, leaning forward feels extremely awkward and they will avoid it at all costs.
What ends up happening when you don't, is you pick up speed very quickly in-between turns because you lack the forward pressure to push the turn through. Since the turn isn't being made and you can't bleed off speed, you get out of control very quickly.
It's hard to fight the impulses your mind sends you that your body is out of balance, but you want your center of gravity (body) northeast or northwest from the center of the board.
This is a poor example pulled off the google to give you a visual: See where his body is in relation to the board? You probably won't be leaning that much yet, but basically the further over you get the more force you have to reel turns.