um how long have you been quilting? I think your too hard on yourself, I am not meaning to offend you..........remember when you remove a seam even very carefull there is some stretch that will occur. In addition quilting involves mechanics too, cutting your fabric and even where you sit at your sewing machine. Sitting slightly to the left or right of your needle can change your sight even 1/8 th of an inch.
Perhaps you need to hear me say..........it will never be noticed by a man riding by on a galloping horse..............and like a previous post, the PP method is very acurate and that your work probably isn't shoddy or sloppy..............take a breath.........skills will improve..........your math skills are needed in my household now..........with a quilting pattern written for 6 blocks.............girls .....however I want them in different dresses....................sheesh..............I was a dreamer in algerbra................calla...............hee hee hee