What to expect from my new puppy.?

I just adopted a new puppy this weekend. This is the first new puppy I have had in almost 15 years. She is 1/2 American Shepard and 1/2 Bull Mastiff. The guy I bought her from says she will probably be about 60 pounds, but that seems kinda small to me. Her mom is the mastiff and weighs in about 90 lbs her dad is the American Shepard and weighs about 60 lbs. I have read up on the breeds and from what I have found they say that the Mastiff should be between 90-130 lbs and the Shepard should be between 70-85 lbs. The dog looks just like a mastiff execept for the coloring is not like a pure bread mastiff. I think the guy was under estimating her size to get me to buy her. I don't care how big she gets, I just want to know what to expect. Anybody have any ideas? I will be taking her to the vet in two weeks so maybe he can tell me more, but I am curious now.