I am not quite sure what went wrong with the net calories
But the 644 cal/day is probably based on the amount of weight you want to lose calculated over the amount of time you want to lose it in. Did you enter your current weight and activity level in our profile?
If so, you might need to change the time to lose the weight. As I am sure you know 644 cal/day is very low, and almost impossible to maintain for very long.
Check those things and write back if you are still having problems. I or someone else will jump in to help.