I've made 20 or so quilts and am still waiting for things to be "accurate." In fact, I'm just coming back to quilting after taking a vacation from it for a year or so. One of the reasons I stopped is because of all the little inaccuracies in my work, knowing I'm still having the same problems after 20 quilts is very frustrating. I go slow, I measure everything twice, I'm careful, I have the correct tools, I watch youtube, yet things are still wonky, my seams are off a hair or 5 here and there which at the end of a row makes a difference.
Last week I watched several youtube videos on making quarter square triangles. I followed the directions to a tee. Yet in the end just about every one was wonky and now I am doing the daunting task of cutting every square down to 3" because 3 1/4" wasn't working and even with this I'm finding some of the squares are short by a sixteenth of an inch or so. And I know when I finally get the pinwheels together, even at that point after all my careful measuring, things will be wonky again. By the end of a quilt I'm usually so fed up with my crooked lines and borders I want to throw the whole quilt in the attic. From a distance things looks fine, especially after washing it when things seem to fluff up a little and inaccuracies are hidden but if it were to be judged, I'd be doomed.