You have to be sure that the fabric is lined up on the straight of grain. Many times the edges are not cut evenly at the fabric store. One way to check this out is take a piece of fabric - about 1/2 yard by width of fabric. LIne up the selvedges. Hold the fabric up and grab it with your fingers. Move the selvedges from side to side and look at how the fabric shifts near the center fold. Don't focus on the edges. When the fabric lies perfectly straight without wrinkles you have it lined up correctly. Place the fabric down on the mat, being careful not to shift it. The take a ruler and trim off the edge. Be sure you have the ruler perpendicular to the fold. This should eliminate the "dog leg" or as some people call it, the dreaded "V"