Guess what? The world won't collapse because you had a little naughtiness. You don't say what kind, but that may be for the better!! All you will have done is stall things for a bit, not forever mind!, and give yourself the most almighty guilt trip. Former will soon be rectified and latter will do you good.
Recognise what you have done and why you did it. Was there a trigger or just a sod it moment, learn from it and move on. On LLL, you could actually enjoy a BBQ without being naughty at all, all that salad and a bit of protein. It's the will power to resist all the other things you have to hone!!!
Glad you'd moved back on the waggon though. Each day is a new one and a bit closer to your goal. Just don't fall off again if you can help it, it pushes the goal day a bit further away.