London underground oyster card question?

So if i get the train from barkingside to stratford and drop someone off (but dont tap out) and then get the train back from stratford to gants hill (back the way i came) - would i be ok if a ticket man came to me and to exit at the barriers because it would mean that ive taken around 50 minutes to make a 5 minute journey? if i said i overslept past my stop and came back would it be ok?