Clearly your answer doesn't make sense. I think its because the 3.5 lb you lost isn't all fat, some of it is water weight, and your calculation assumes it is all fat. Especially in the early phases of a weight loss program, much of the 'rapid' weight lose is water weight. BUT, clearly your weight is coming done, and clearly 3.5 lb can't be all water weight, so you are losing fat and meeting your goals, so just keep doing what you are doing and BE HAPPY!