Probably not. Count it as a flexi day and keep to the plan for the rest of the time. At the end of the day, we all have to live our lives. We can't spend every second totally focussed on diet. Sometimes other things happen that take centre stage. Don't worry about it too much, but also don't let it send you into that "sod it, I've already blown it so I'll just eat whatever..." headspace, as that is a slippery slope!