I am assuming that the erection is long gone and that the veins appear more prominent than previously. I can only guess that there was some swelling in the skin from the ring (especially if the ring was left on for a long time) as well as local trauma from the rough stroking. I expect that everything will return to their previous state in a week or so.
A constriction ring should not be left on for more than a half hour.
S.A.Liroff, M.D.