When's your weigh in day? If it's Monday, it might not help, but whenever it is, if you stick to plan 100% until then, and perhaps have some SP days, and only have 5 syns a day, the good should outweigh the bad and you could still lose.
It sounds like you've only had 3 meals off plan, so you hopefully still have 18 meals on plan. So you could still lose, but even if you do show a gain, it's not necessarily all fat, it could be fluid.
Just keep going and do the best you can - as hugo says, it'll come off eventually - it's not a race and we have to learn to cope with such events.
Stay to group and when it's your turn to talk, ask for help with dealing with social events. If you have any control over the food served, make sure there's loads of lean meat and salad - have you tried the SW range at Iceland - there's burgers, sausages and meatballs that are all syn free. Plus you can do things like marinated chicken breast etc. If you have bread and cheese make sure it counts as your HE choices.
For alcohol - try and alternate with still/sparkling water or diet soft drinks. Spirits and diet mixers offer the best 'value' syn wise - ie the most booze per syn.
Also think of your syn allowance as weekly. Eg have 5 syns per day for most of the week, this means you could easily have 35 a day on Friday and Saturday and stay within the 5-15 a day guideline on average.