another thing that can cause distortion even though you dont' notice till its' too late...when sewing multiple pieces together that seam allowance is important...if you are off just 1/8", doesn't seem like anything at all, but then when the 8th piece goes together...woah...you are a whole 1" off!!!it adds up and isn't noticed until it is too late. pressing is important, sometimes if you 'square-up and trim your piece after each addition it is more work but will help keep everything as it should be in the end.
i had a little lady ask me once...when i was complaining about the imperfections in my latest piece..."can you see it when it hangs off the brooklyn bridge?" in other words...we know the imperfections are there because we've been UP CLOSE all along...anyone else looking at it is not going to notice what we see as a glaring boo-boo. so unless it is to be judged and has to be perfect don't sweat the small stuff, no one knows but you :mrgreen: