biggest loser creche style

I've just joined the biggest loser though my son's creche. I think it goes for 12 weeks. and I get weighed every Thursday (well first weigh in tomorrow then thursdays)  the deal is, if you gain, you pay $1 per 100 lbs. so if I gain 1 kg, theres $20. if you lose you dont pay anything. the person who loses the most at the end of the 12 weeks wins most of the money from the kitty, and the 2nd and 3rd get a cut. sounds jpretty straighforward. hmm... and could be the kick in the butt I need