First of all, have you stuck to plan this week? Or have you been off plan? There must be a reason why you feel like you have not lost any weight. You may not look, or feel as though you have lost any weight, but this does not mean that you haven't - how will you know unless you go to weigh in?
Weighing in once a week is all part of the plan. Without weighing in weekly, you are not truly sticking to the plan. Besides, what is not weighing in going to acheive? It won't change this weeks result, whether you weigh in or not.
Also, there is no problem with having a Mars bar - aslong as you Syn it. Have you Synned it? The plan is structured for us to be able to fit in little treats like a mars bar here and there. On the other hand, comfort eating because you 'feel' like you haven't lost any weight is not the way to go. If you carry on that way, I'm pretty sure you won't lose any weight.
Stop being silly, keep following the plan, and go to class. You will soon reap the rewards.