This has happened to me on numerous occasions. I think I am doing really well, and lo and behold, the scale jumps a couple of pounds up from the previous day. It just happens some times. Don't forget, your body is getting used to the new habits you are forming and sometimes will rebell against not getting all the foods you were feeding it before.
As for weighing in...I weigh every morning because that is the one incentive that really works for me. When I see the scale moving backwards, I am happy for the day, if I see it has stayed the same or moved up, ugh, I make a new committment to losing those pounds. I don't think missing one day at the gym will set you back.
Hang in there. Just keep following the rules. It is tough for us bandsters at times. (I just keep thinking of the end when I shed all the excess poundage...TUMMY TUCK, TUMMY TUCK, TUMMY TUCK)