If you are right handed practice holding the ball with your middle and ring fingers at 6 o'clock and turning the ball counterclockwise to 3 o'clock when releasing the ball.
The above is counter to a full
roller release in which you may start in a "handshake" position with the fingers at 4 o'clock. However when releasing the ball, the hand moves clockwise instead of counterclockwise resulting in a full
roller.
If you have an old chair a home you can practice turning your hand in a counterclockwise direction at the release point. Remember that the turning is done with your arm, not your wrist.
You are driving your fingers through the ball, not around it.
Also, if you haven't done so already, have your thumbhole drilled with under the palm pitch - 1/4" maybe. Under the palm pitch will help you turn the ball counterclockwise.