If you don't want to take it in, then take it apart.....lay you machine on a towel, unscrew the bottom, check for lint, gunk etc. Clean any debris out. Turn the hand wheel slightly toward you to see any obstructions. Is your back stitch a button or lever? You may need to remove the entire cover to see the back stitch mechanism to determine the sticking in reverse. Feed dogs could be gunked up.clean that area. Best wishes to a quick fix.