Rory was huge when I got him at 11 weeks. 7lbs. He is now fully mature at 2 years and about 17.5lbs. I was sure he would be gigantic! but he is perfect.
Also - interesting thing I learned in reproduction class today. The size of the fetus is limited by the mother's ability to provide nutrients via blood flow, etc, which is in turn limited by the number of puppies. More puppies - less nutrients per pup. So larger litters could have smaller pups at birth. Also - if a great dane male impregnates a chihuahua, the fetus will be limited in its in utero growth by the chihuahua's ability to provide nutrients - so even though the genes will provide for a bigger dog, it will be born chihuahua puppy size and then do all its great dane size growing after birth.
Dogs are not our whole life, but they make our lives whole.