Proper sight alignment is very difficult if your aiming eye is the wrong distance from the rear sight. This is called eye relief. Eye relief should be about 3 inches when you are in position. If you are closer, the rear aperture will look too big and you wont be able to center the front aperture easily. If you are too much farther from the sight, the front aperture will look too big making good sight alignment very hard to do.
Your head position must stay the same for each shot. You have to find the right place for your head so that the rear aperture is a full circle. If your eye isn’t lined up with the rear sight the hole in the sight will have a square side. If you don’t see a perfect rear circle tell your coach so that some adjustment can be made.