It is sometimes nothing you did!! (Some wise quilter told me this once and I so thank her often in my thoughts!!)If your cutting board isn't all torn up, and your rotary cutter is cutting thru fabric w/one swipe (or it is dull) and you know that your ruler isn't sliding...it could be NOT you!! But, the pattern!! It does happen and I did have that happen to me once and no matter what I did...it didn't come out exact in measurements as said in pattern...:)One other blessing for me was my 1/4" presser foot that has a guide...! Such a blessing that little creature is to me!!:)Do keep us posted on your findings...and, just don't give up...:)Skeat