It's actually double the weight at
twelve weeks.
No way is your puppy even close to her full grown weight at only eight weeks old. If you look here, you'll see she is off the growth chart:
Yorkshire Terrier - Yorkie Puppy Growth/Weight Chart - watch us grow
Did you actually see her parents? Even if they are small, since she is a mixed breed, she may have inherited her larger size from her Poodle genes. Genetics are tricky even in purebred dogs.