This has been one thing I rarely get right in all the years I have been doing it. No matter how many times I fold and refold and smooth and recut I rarely get it to go straight without a v in the middle. For wide piece, borders for example, I always tear but when I need to cut the 2 or 2.5 strips I spend most of my time refolding and recutting and putting crooked strips in the scrap box. I have 2 18x24 mats, one omnigrid, one olfa and had one of the bigger gray mats(which killed my blades quicker btw) . I guess all of us has one thing that is just a bear to us.