You mention the pup is 11 inches at the shoulder? that seems quite tall for a 7-8 week old pup. Especially since a full grown American Stafforshire Terrier and most American Pitbull terrier's (unless gamebred) only get about 18-22 inches at the shoulder full grown
I havent measured the Newfoundland pups at 7 weeks, but, I'm know they are not that tall at 7-8 weeks.
If she seems healthy and has had a good clean bill of health from the Vet then be happy with your pup. Make sure you put the pup on a good food, Innova, Karma, EVO, Wellness, Eagle Pack, Canidae etc. and socialize the pup properly. Don't worry about the size the pup is going to be, just as long as it is healthy. The worst people for ruining the health of a dog is the ones who feed too much hoping they get a big muscular big boned dog when it grows up. Nothing could be further than the truth
A pup is genetically coded for the size it will be when it grows into adulthood. Even a slightly malnourished pup will grow to proper size that it was genetically coded with.