Keep practicing like the others said, treat the ball like a baby, you'd want to put the ball into the hoop gently. If you hit it too hard you'll miss. Also, if a full speed layup is too tough, I'd suggest taking a huge bounce and hopstep near the hoop and lay it in normally. It's more stable and it's easier to pump fake if there's a big man on help defense. But despite this, you still gotta master the full speed layup. Get comfortable with scoring the layup before incorporating it full speed. Good luck!