Try heavily starching the backing. I use a 1:1 solution of Sta-Flo liquid laundry starch and water, "paint" this solution on using a large wall painting brush, wait a couple of minutes for the solution to penetrate the fibers, toss in the dryer, then iron with steam. I do this to the yardage before sewing into a backing, but you can also do it on the completed backing. Starch stabilizes the fabric so it is harder for it to fold over on itself.
Also, spray basting is easier than pin basting and allows you to peel off and re-position part of the quilt to get rid of a wrinkle. The only basting spray I recommend, though, is 505 and you do need a well-ventilated area to work (outside on a non-windy day works well).