Can you post a picture?
I hate to say it, but sometimes rulers can be off just a tiny bit, and it will end up causing quilters headaches. I never thought to look carefully at the markings and corners until one day, I was doodling with pen and paper and a quilting ruler. I was drawing radiating squares and after 8 or 9 rounds, realized that they were not all even. Took a closer look at the ruler and discovered that the very first 1/8" line was either printed wrong, or the ruler was out of square by what would be only 2 or 3 thread widths. But to a quilter, 2 or 3 thread widths can throw everything off eventually. Quality control either didn't notice, or didn't think it was enough to bother with. I took the ruler back to the store I'd purchased it from and looked at all the other rulers that were identical - every single one of them was off. Very disappointing.