If you get discouraged because things don't measure up when you are finished, try paper piecing it. You can use freezer paper and do it piece by piece or if you can break it up into sections were it would work with one done to start and add others to the same paper piece. This way the fabric does not stretch, you have perfect seams and it all fits together perfectly. I took a class once by Shar Jorgensen and I was extremely frustrated with seaming things and having them come out perfectly--she is a real stickler for this. Paper piecing makes everything perfect by stopping any stretching or bias changes. It always measure perfectly in the end, the seams are perfect and straight. The trying to get things to sew together perfectly without it can be done on your own time with scraps or on a project that isn't costly--if you do not want to paper piece, you may want to starch everything real well to avoid any stretching.