You should be aware that you need to "pull through the shot" whether there is any actual movement of your drawing hand or not. "Holding" at full draw is kind of a misnomer, since you have to pull just as hard to hold a shot at full draw as you did when you were drawing the bow. If you don't, your drawing hand will creep forward, your shoulder might sag, and your shot will collapse.
So if you don't feel like you're getting a good anchor, you can slow your draw way down, or even stop the actual movement of your drawing hand, and still be pulling through the shot.