Don't be too hard on yourself. The key here is, that you're right back on track today. This is how it's going to be through the rest of your life; allowing yourself a little something off plan on occasion, but then hopping right back on track.
I was banded on 3/25/13, and decided that the Memorial Day BBQ I went to, would be the day I allowed myself some wine. I hadn't had anything to drink three months prior, and thought one glass would be all I could tolerate. Not! I think that I drank damn near an entire bottle! I tolerated it fine, but didn't feel very well for a couple of days. Not sick; just off a shade or two. I'd like to say "lesson learned", but I'm sure I'll have a day like that again. Felt NO pain & had a great time!!