The pin method is what I use to keep my seams straight too. I had to practice on it before I really got it down pat and sometimes I still have to pull out my trusty seam ripper! I put the straight pin through each of the seams I mean when they come out on the other side they have the outer edge on both sides-I've really divided the two fabrics. Then I keep that there and pin on each side and then on the ends.......then I take the straight pin out. You probably know more than do so please just know that I am just explaining how I do it.