I don't know how low carb works but there's 3,500 cal in a pound of fat so that should mean you have to eat that to gain a pound :/ but it hasn't been the case for me when I cheated, though I was told some of it's water.

If that's you in the pic, you look pefect! I wouldn't worry so much and just dust yourself off and get on with business just don't panic or eat yourself up over it!