Hi, Welcome to Global Paw!

Congrats on your new pup, I hope you'll post tons of pictures of her in our picture forum for us.

We LOVE pictures.
I've never had a lab so I'm not sure how big they should be at 8 weeks. You could try googling Labradors and looking at some breeder websites to see what their puppies looked like and sometimes the breeders have the weights of their pups recorded there too (not always, but you never know).
Enjoy the site, and if you have any problems or are unsure about anything, feel free to PM me or one of the other dog forum guides (DFG).
Cass.