Of course! The chance is that you will eat more calories on this day than if you follow the plan. You can still make conscious choices. I often choose a starter and main course, of which I can roughly estimate the calories. I skip dessert and choose a zero drink instead of wine. You could also go for three courses, of course. Don't be too hard on yourself! A nice evening out will do you good, and you can always eat a bit more the next day to restore the balance!