Do you know what, 3 mini cupcakes is really not that bad compared to what you could have eaten! I know if it was my birthday I would have been off plan from the minute I woke up to the minute I went to bed.
If you are out of ketosis then don't worry, you can get back there. Considering the occasion I think you were very restrained! Best of luck for WI today - I hope the scales are kind to you X