Did anyone consider that the stock may not be square, recoil lug inlet off to one side, or a small piece pf plastic keeping it from centering.
Try this also place barreled action in stock, hold it centered then tighten front screw snugly then rear screw, then torque front then the back and see if it helps.
If not it is only cosmetic any way, pick up a set of windage adjustable bases and have it.