demoniendin

I recently went through the second shed with my ball python. It was about two weeks ago. The shed appeared perfect to me at first glance, but now that hes pretty much digested his food from last week and im able ot take him out with little stress on his part, I noticed that his nose has turned a greyish color and a couple of individual scales on his back have also. After reviewing the shed which ive kept, ive noticed that the very end of his face wasnt completely shed and there were tears along the back. personally i knew about the tears but it didnt phase me that they were from retained scales, i simply thought they were just mishaps with the shed. So anyways, what can i do to treat this and how can i make sure it doesnt happen again?