Hi
You haven't 'been bad' you just chose to have some food, don't be so hard on yourself.
I find that weeks like yours do happen from time to time, not sure why after being so successful we suddenly give in to our cravings. Of course once you start it's much harder to stop especially as often after eating you can feel a bit queasy which we often mistake for hunger and so eat again, Downward spiral really.
I think it's good that you have your WI tomorrow, never mind that you may not have lost or even had a small gain. By weighing in and having it written down black and white it will be an official line drawn under it and a fresh start. Hopefully then you won't drift on for another few days.
At least it's only been chicken that you've gone for and you haven't thrown in the towel completely, you have shown a lot of restraint and I expect the damage is minimal.
Good luck at the WI and I really hope you get back on track, I'm sure you will. If it's just not happening for you why not have an Add a Meal Week that way you'd probably feel more in control.