Stockinette is a pretty tought stitch...it doesn't want to give up the roll very easily. I think that sometimes it does require more than 3 stitches on either side to keep it from rolling. not sure what a good number is though. I am inclined to do a stockinette stitch scarf in the round so that i don't have to worry about it.
probably five on each side might be your best bet.
Not sure about reversing the pattern but logically i would THINK that would have to work.