I never wash my fabrics before I use them and I never had a problem with shrinkage, and I have washed my quilts many times. When I get my purchased fabric home, I steam press it all and organize it until it's ready to use. Plus I always use steam to press open my seams., the trick to useing steam is to NOT slide your iron back and fourth, (that is what stretches your cut pieces), especially triangles. When they say PRESS open they mean just that. (To hold your iron down and press),
but not slide it back and fourth across the fabric