well it stretches because one is being "worked" harder than the other. I don't know that i would give it too much of a tug though because it is easy to get into the habit of doing that and start knitting too tight. When you stick your needle in the next stitch and work it, it should work itself out.
as far as whether you get both stitches knitted or not, it is possible to have your work have the right count but that stitch still not be worked. Look where you have done the decreases and see if there are any little holes there (besides the stretched fabric of course) ...if there is, and the little bump is still there it is possible that one of the loops may not have had the needle go through it. just watch and make sure the needle goes through BOTH stitches and one isn't just getting pushed off from the force of working it.