In my personal opinion, yes

As long as you eat well MOST of the time, then you are already doing something good for your health and your weight. Life happens. Special occasions are a part of a happy and balanced life. I think that was touched on in the book, though I don't have mine handy.
If you eat well from now until then, chances are that you will not go far off track that night anyway. You may want to eat smaller portions, or choose something healthier from the menu. Share a dessert between you

You can still have a nice night out without overdoing it.
Good luck, and have fun!