Hi and YES there is a way around this type of dilemma! Couple ways to approach it, or multi-approach may be better. First, you do want to PLAN AHEAD for days like this, and there are a lot of them, in order to continue to be successful. You can start by being sure you have 'saved' enough calories in the day, so that your total for the day isn't too far off; and you can do some extra exercise - but that alone is not the best way to lose weight as you can never outrun your diet; and you can just adjust your thinking that what looks good for a moment is not going to get you to your goal and learn to adjust your thinking about treats.
There is no way a person can attempt to get through life without some playtime, including an occasional treat. But you want to be smart about it and to recoginze that big word "occasional". You said this isn't your birthday - do you plan to go all out on your day, or just indulge in a little treat like a drink or a small dessert? And think about the upcoming holidays too, known to throw the best of us off track!
Know in advance, plan your day, decide what YOU WANT out of the day so you have no regrets. And remember if it's just one day, you dont' have to throw in the towel. Get back on track, record everything (I use myfitnesspal but it looks like my new fitbit allows that too) including the food you didn't mean to have, get out and exercise and keep your eye on your goals. Good luck to you!
