Well those pups are cute any way...There is no knowing the size... I know one woman on here said her puppy was much biggerr then both parents. The parents were 4-5 pounds and her puppy grew to be like 9 or 10 pounds.
What ever happens I'm sure your going to love your new puppy to death! I would call though. If these people are going to refund your money the sooner you tell them the better.
try to be open minded and see whats meant to be. Maybe this pup is the best thing that ever happened to you!!!