Baps, the best thing you can take from the weekend is how bad you are feeling now. Other than that, it's done now, just get on with the job. If you don't lose much this week then mark it up to experience.
You aren't the first to slip up and won't be the last, just read other posts along the same line. I won't pretend you will lose as much as you may have otherwise but forearmed is forewarned! Expect the worse and you maybe pleasantly surprised.
Good luck with your WI. I do hope you lose and are happy. Life is sent to try us and we need to kick back! I'm lucky with the support I get from my OH and children and at a recent barbeque everyone else thinks I ate but in reality all the food on my plate went to my children - bless them! The other people there don't know what diet I'm on and I have no intention of telling them. We need to develop strategies for dealing with these situations.
Onwards and downwards (weightwise!)
Good luck hun.
x