Riders who get ahead of the horse's motion at take-off are often anxious riders who are using their upper bodies to motivate the horse, rather than properly using their legs. You should get into two-point position during your initial circle and stay there throughout the entire course. Concentrate on pressing the horse forward with your legs, rather than using your upper-body as a motivator. This way, you can stay still in your upper-body, making the performance look effortless, while using your legs to do all the work.
Be sure not to actively close your upper-body at take-off, but instead, let the horse's jumping effort--that is, the arch of its back in the air, or "bascule"--close your hip angle for you. Also, if you're riding a tense horse, don't let the horse's anxiety cause you to close your upper-body ahead of the motion, for this will actually make the horse more nervous and quick. Just in the same, still, two-point position around the course, letting the horse's jumping effort close your hip angle ever so slightly in the air. That is all you need to do to stay with the motion of the horse.