Crashnquilts is correct about the fabric. I don't know if any of you remember buying cheap jeans in the 70-80s but they looked great at the store. But the first time you washed them one leg would warp and the seam would drift from the side of the jeans to the front and back. This is an example of the weave being off. Washing the fabric first is a big plus. I don't rip, but I take one or two threads, and just pull them enough to be able to see the change, and then cut along the threads to get the straight of grain. Then I lay my fabric smoothly out on the table smoothing out from the fold. If my grain is straight than the end that I just cut, should be really close to both selvedges. I find that if it is 1/2 inch or less off, it is no big deal. however i have found fabric that was close to a foot off, and that will make a huge deal in your larger quilt pieces. Then you need to get a friend and start at the bias and start stretching it back into place all the way down your piece of fabric. Sorry this is so long.