Oh lemontart I know how you feel, been there done that.
What you do over Christmas is entirely your choice. Would you prefer to say s*d it completely and have a fresh start on the 1st, having got the most tempting period of the year and all the cravings for naughty food out of the way, or would you prefer to damage limit and be moderately sensible whilst accepting that you aren't going to stick 100% to plan? I get the impression you're in no mans land, doing what I've done all year and eating the right foods but the wrong ones too.
My advice would be either be a bit sensible, so plan in advance... if you're going over to so and so's to visit, allow yourself say 5 chocolates or 1 mince pie or one slice of cake - something that you think is realistic and achievable. Eat food optimising foods where possible, and BANISH THE GUILT! If you're like me, feeling guilty only makes me comfort eat mroe anyway with a "oh well I've already blown it" philosophy, so if you say "ok I'm allowed 20 syns a day" or 2 mince pies a day or WHATEVER level you feel you can realistically stick to, at least you are still in control at the most difficult time of year.
The other plan would be to say right, stuff it, I'm going to compeltely ignore SW eating until the 1st. Eat whatever you want that is non-SW for your main meals too - that way when it comes to the 1st you won't feel like you've been eating the same foods but been gaining, you'll feel like you've had a complete break and your body will appreciate the change when you come to sticking to it again.
Whatever you choose to do, make a decision, stick to it and DON'T FEEL GUILTY ABOUT IT! we're all only human.