Notice the opposite side of the pieces you are sewing. If they don't match evenly together then no matter if you match at the seams the row will be crooked. I always match the opposite sides of the seams and that may mean I have less seam allowance for one fabric piece for the seam. If it is more then 1/16 less then I know I messed up somewhere. I stop and find out why before sewing more. I took Sally Collins class and it isn't for the hurry up and sew type people. Each step is very precise. She had a video class on The Quilt Show last year which was excellent.