Drink as much water as you can, then forget about it and stop worrying.
Popping out of ketosis briefly is not the end of the world - what makes the difference is what you do while you are out.
If you have popped out of ketosis you may feel hungry tomorrow - possibly ravenously hungry with cravings and headaches similar to what you had when you first started CD. If you give into these cravings and eat more carbs then you have a problem.
All you need to do to stay on track is to wake up resolute tomorrow - stay on your plan whatever it is, with a little extra water for good measure, and ignore the cravings until they go away.
If you can do that then your weight loss should not be affected & you'll be back in ketosis in no time.
This is personal (successful) experience from the girl who ate a large hot dog at Thorpe Park in Week 2, but still lost weight.