Is this a new problem or has it been like this since you got the rifle?

If it's a recently emerged problem, has anything changed with the inletting? I'd look for obstructions inside the stock that may be pushing the receiver into misalignment. I'd also check the recoil lug to see if it's come loose and reset itself off-kilter.

If it's a persistent problem, check to make sure the barrel channel is straight or at least the same on both sides. It's possible that the stock came out of the mold incorrectly, which could be a factory fix. Same advice would apply if there's a manufacturing defect in the inletting like a bulge where there oughtn't be or a mishapen pillar.