What Causes Shrinking Of Penis In A Child After Circumcision?

My 5 mth old son was circumcised. He is a bit of a chubby baby but since the operation his penis has sunk in and hides. When we bath him we pop it out to clean it and during most diaper changes. It just turtles back in. Is this8s something he will grow out of? I have read this might be a case where the circumcision was done too far back.
Should I be pushing the skin back regularly to stretch the skin?