My guess is that the app is giving you negative calories because you are being unrealistic about your goals. For example, if you want to lose 50lbs in a month, that's not going to happen. The app didn't give you a budget because the only way you will lose weight with the goal you set is if you don't eat. Try setting a more realistic goal. For myself, I want to be down from 220lbs to 150lbs but I gave myself until August of 2014 to accomplish that.
Ok so i realized that i messed up i thought it ask how much u want to loose not how much u want to weigh maybe i will figure everything else out