Umm, I've always been told not to use the mat to measure with, but I must confess I use mine at least to line it up and then use the ruler to cut. How about if you used a fine sharpie to write the correct numbers under the incorrect ones? Or maybe every other one rather then all?
It's interesting, I just bought a new mat and haven't used it much myself, I need to check and see how the numbers run, I bought an Alvin after I saw glowing raves, here I think.