I know how everyone feels. One thing that has helped me is...even when I go totally off track (i.e., eating a whole cadbury bar on V-Day even after Mexican food for dinner) I try to think about what I did good that day. And that particular day, I did *not* buy a candy bar from the vending machines at work. I did not drink soda with my mexican food. Sure I was about 800 calories over my "range" but add in an extra candy bar, some soda, some horrible snack at work...could have been much worse!
You have to think as every bit of bad food not eaten, or each good choice, as a step in the right direction. You said you did good until 2pm, and that you walked for a half hour. Those are excellent! 2pm is past lunch, over half your day! Sure, dinner wasn't everything in *could* have been, but nothing ever will be. I think you had a good day because you exercised AND you did good up until 2pm. We are always our own harshest critics, and while it's good to strive for perfect sometimes you just have to take what you can get. If it's only one bad meal, or only one bad day, or only one bad week, or only 1 bad year, or 1 bad decade out of a LIFETIME than it's nothing compared to all the good you will do and strive to do.
"What would you try if you knew you couldn't fail?"