Can I please suggest you check that you have the correct bases and that the rings are around the right way, as in the correct one is at the front and rear, the rear of the scope should be higher than the front.
To centre the cross hair, all you need to do is wind it one way all the way until stops, then wind it the opposite way all the way and count how many clicks it takes, halve that number and wind it back that number, do both, windage and elevation.
Cheers.
