You will get, I think, the same answer from everyone else. Stop weighing in-between weigh ins. It doesn't mean anything. It's different scales. It's a different time of day. There is a reason you're advised to weigh once a week at the same time of day. For consistency. Weight naturally fluctuates throughout the day/week according to meals/fluid drunk, fluid retained, how many times you've been to the loo etc. Only the class scales count. Also, it can sometimes take a couple of weeks for losses to show up.
Because of the inaccuracies of sneak peak weigh ins, unless you're capable of ignoring the scales and taking it with a pinch of salt, you should stop weighing at home. And I think you've proven that home weighing is having a negative effect on you. Already you feel down and don't want to go to class. The truth is, you've probably not gained. But even if you have, you would be one of those people who really needs to go to class, get motivated and get the problem sorted out, coming back with a bug loss the following week. But the home weigh in has made you feel you can't go, which is the slippery slope to not going at all, not sticking to plan properly because you're down, "why bother now because it's Xmas", gradually going back to old ways and ending up gaining more than before. I know that sounds like I'm being dramatic, but I'm sure most of us here recognise this cycle.
You would have to have consumed 3500 calories more than you need this week to put on even 1 pound of fat. So in all likelihood, your scales are misleading you. But supposing you have gained, so what? We're all in the sane boat. Every week, some of my class have gained. Ignoring it won't make it go away and denial is a river best left in Egypt. My advice: stop home weighing, stick to plan 100%, reread book for reassurance and give yourself a kick up the bum and get yourself to class. Deal with this hurdle as you mean to go on
