You didn't say how the slide went forward before you dry fired. In normal functioning, the slide slams forward with considerable force to reach true battery position. It certainly isn't 1/10 inch out of battery. Thus, the slide isn't gonna boogie about-at least anywhere near as much as you suggest.

Having worked with a slew of people during transition training to the M&P series, the most likely explanation of your errant shots is your incomplete mastery of the trigger stroke. Continue your dryfire with your attention on your sights and the target, not the slide. Also work on your grip, it should be firm with tension from the support hand.

To paraphrase a well known trainer, "It's not the arrow nor the bow, but the Indian".