I'm trying to sort through your number and calculations, it's kinda confusing. The only thing I could think of, and it might seem a really simple answer, but could it be that the 3.5lbs that you lost would include normal fluctuations in your weight on a daily basis? I find my weight fluctuates between 134 and 137 on a daily basis, even if I weigh myself the same time everyday. Could it be that part of your 3.5lbs weight loss included some of this fluctuation and you actually lost less than you think?