Have you checked your 1/4" measurement....using the three strips, sewing, measuring? The " mark" that guides your seam sewing is vital to correct-size blocks..not to mention, of course, accurate cutting.......
Some days I get what I call "sloppy" ........ That's the time I stop and re examine my seam guide, my cut pieces and finished block to try to find out what I did carelessly.....makes me get back on track......and realize that to get a good finish I have to slow down and concentrate on what I'm doing......or just leave and do dishes or something!!