Originally Posted by irishrose
You need to have the folded edge lined up very straight with the edge of the ruler closest to you. Not a perfect 90 degrees is what causes the wonky vees in the strip.
Irish Rose is quite right. I use the lines on my cutting mat to make sure the edge of my fabric is straight, then, I use the shape cutter to cut my strips. I will even line up the horizontal lines of the shape cutter to the horizontal lines of my cutting mat (below the fabric) to make sure the cut is accurate.