When I signed up I told them that I wanted to loss 40lbs. They told me I could do this is 14 wks which would be about 3lbs a week. I have averaged 2 lbs a week. Do I have to pay for additional time if I didn't meet their average? Can I just postpone my stabilization until I hit my desired weight without an additional fee?

You'll have to sign up for additional time unless you've been perfect to the contract and the guarantee applies to you. I've never had the guarantee apply to me...sooo I've always had to buy more time. Usually thats 10 weeks minimum, but ask when you get to the center and see what they say.