Keep both eyes open, concentrate on the target then pull the scope into your line of vision. Don't change your focus off the target. Don't look INTO the scope look THROUGH it. Move the gun until it is in the right place. Not your head.
Remember as the power goes up the exit pupil get smaller. Making harder to center.
Also one more thing, Are you right or left eye dominant? If you are left-eye dominant shooting right handed it is harder. You will have to practice.