I have trouble with painters tape shifting as I stitch, so I now draw a line with a water-soluble pen or chalk, beginning at one side and continuing to the other. I pin baste - don't like spray glue. Contrary to all advice, I usually don't start in the middle and find it all works out pretty flat if I just continue parallel to that initial line. I hold the quilt lightly so as not to stretch any bias.
You might also try doing an initial basting up and down (perhaps along any sashing) with wash-away thread just to make sure the quilt doesn't shift.