Sounds as though you will have to shim the back of the scope. I always try to shim at the scope mount, but sometimes it cant be done. Shims can be made from a soda can and a pair of sissors. You will want to take the mounts off the rifle and lay some shims between the rifle and the mounts (in your case the back) then reinstall the mounts. If you have been sighting at 100 yds, try 3 shims to start. You can add or remove to get you back on. Be sure to recenter your scope adjustments first.
No such thing as a stupid question. What is stupid is not asking it.