I'm just guessing, but your biases may be running in different directions. Your material will stretch one way but it won't stretch when you turn it the other way. Try keeping the biases all one direction. You have to sew with an accurate 1/4" on EACH & EVERY seam. Say you're off 1/8", & those 1/8" keep adding up, it will throw the seams off also. Accurate cutting is a MUST. With my first quilt, I cut mine with scissors, drew the squares out with a yard stick. No, I'm not that old, I just didn't know any better. Using a rotary cutter & a good ruler helps. If there's ANY possiblity of taking a beginners quilt class, it is so WELL worth the money. It is amazing how much you can learn from them. Good luck & don't give up. It's mind boggling at first but there's lots of good help here on this board.