XXL not centering text when carving

I made a sign using a vee mill and everything was shifted approximately 0.17 to 0.2 inches to the left even though I centered it to my stock. I realize there are going to be some slight variations in the boards width which could account for some of this but I would not think there would be that much variation. I just cut two pockets on the back side of the same board that were supposed to be 0.5 inches from the edge but now the left side is 0.58 and the right side is 0.4 from the edge which is again right in the 0.17 to 0.2 inch area. Any ideas. Thanks

Center of the stock — positioned how? off-center measure derived how?