About ten days ago I went through the exact same scenario. Had a bad day, gained five pounds overnight. Except this time it took me two days to do it. So frustrating! I feel like a dumbass, to be honest.
The way I figure it, though, is that I will get right back on program diligently for the next seven days (just like last time), and lose another ten pounds. While I really wanted to get below 300 this round, it looks like I'll have to settle for 305 if I am lucky. I've got ten days left on the diet phase which gives me enough time to do 305. I will be happy and grateful for that. Bottom line is, I'll still be looking at over a 40 pound loss in just under three months. That is pretty spectacular.
In the coming (hopefully warmer) days, I plan to start walking again. Maybe I should set a date? Maybe I should do it today?