Two week Appt

So baby had his two week appointment today and I was told by the doctor that he had not gained quite enough weight. But I talked with a pediatric nurse(she is my neighbor) she laughed when I told her this, she said the really only expect at 2 weeks for then to get back up to their birth weight. My little man weighed 7lbs and 10oz at birth and now weighs 8lbs and 11oz. Should I still be concerned about his weight and supplement him with formula like the doctor said?