Grifter, it is good you are looking to improve, but don't feel bad mate, a good friend of mine use to have an average sex time of less than 1 minute, I shit you not.
He once pulled a chick, put in weeks of spadework and bought her drinks, dinner the whole nine yards. Anyway, time comes to 'close the deal' and he lasted 27 seconds (yes we timed him) then rolled off of her said "fuck me that was allright", and fell asleep! I saw this with my own eyes (me and his sister were hiding at the door pissing ourselves) and wouldn't have believed anyone could be that bad, so you have no concerns!