To be off that much, and in that direction, I believe something is amiss in your mounting. Try reversing your rings, front to rear. if the problem reverses, then you may have a ring that is out of spec. If you have had other rings on the same rifle without issue, then that is almost for sure the problem. If the situation is the same with rings reversed, or, with other rings, then you have a barrel alignment issue, and you will need to either shim the front ring as described, or, try adjustable rings, there are numerous ones available. Scope damage using shims is not a problem if you use reasonable torque on the screws, and the amount shimmed is not extreme. I often use a .020" (roughly 20 MOA) shim and have never had a problem. My experience is with PCP rifles. If this is a spring piston rifle, then you could have some scope movement at light screw tension, and you should use either adjustable rings, or, a drop compensating mount (used in reverse in your case).