J.G.
That is a very bizare answer. Is it possible he was just being sarcastic? At my first ultra-sound the tech adjusted my due date about 2 1/2 weeks. She said most likely I ovulated late that month.
You could call the office and speak with the nurse. Perhaps he/she could answer your question. I would definitely try to ask again, but I wouldn't worry too much. Unless there is a problem with the pregnancy and the doctor suggests inducing or a c-section, your body will go into labor when it's ready and your baby will be given a complete physical. The doctors will check you and baby pretty thoroughly.