It's not that tiny. Hans was around 9.5 lbs at 8 weeks, and he was, and is, just fine.
I would disregard the advice of getting him to be 14 lbs by next week.
Slow and steady is the way to grow a large breed puppy.
Don't worry about the numbers as much, focus on slow weight gain, and if the dog is active and growing, then you have nothing to worry about.