I agree with the others that your baby will be a 'teapot'. My Baxter weighed almost 5 lbs at 12 weeks, and is now 13 lbs full grown. He grew in leaps and bounds the first 9 months, then slowed down.
He's much sturdier than Snickers (8lbs) and I don't have to hover over him, worrying about him getting hurt. Enjoy your teapot, they are a joy!