My son was 4 weeks premature and could not be circumcised until he was 2 year old. As like you I thought the doctor left alot of skin behind. However, that was not the case. Even little boys get erections and I believe this is what your doctor was talking about. My son is now 4 years old and he has definetly "GROWN" into his "extra skin". I would not worry about it at all. You will also see depending on if his body temperature is cold or hot or somewhere inbetween, he will have more or less "extra skin".
My son has the same issue- but we took him to a pediatric urologist who suggested he have surgery. I am traumatized by this. I was wondering what you did with your son?
That's only part of what your doctor meant. If a boy is circumcised, when he grows up the penis will grow into the loose skin - possibly to the point where there is not enough to cover the entire thing. This was very frustrating to me, when erections drew the skin really tight as I became a teenager, but I've spoken with others who have had it worse to the point where erections were painfully tight, or even a fair amount of skin from the scrotum was pulled up the penis.
Doctors haven't quite gotten the message from some of us grown men complaining about this. It's still unnecessary surgery, and they shouldn't be doing it.