way to go on 31 days. As others have said, play the tape forward to tomorrow. Imagine how you will most certainly feel then if you blow it tonight.
Feelings pass, that's all they are. Once you have firmly decided you are not drinking, the feelings tend to pass and you can get on with your evening. its only when you are considering doing it that the struggle ensues. 31 days is great, don't let it go over an evening that is just that, another evening.