Barb in Louisiana

I am right handed and cut everything with the extra fabric to the right. When I was learning, I was measuring the fabric on the cutting board and then putting my ruler down on the extra fabric and cutting with my measured piece loose, which meant my extra fabric was to the left side. I found my cutting was very off. Then a friend told me to put my ruler on the piece that I measured and use the ruler lines for measuring accurately. My right handed cuts have been much more accurate, but I can still manage to slide the ruler a bit to the left at the top if I am cutting a full width of fabric. I have to re-square up every 3 or 4 cuts.