Nell, a meringue is not the end of the world, it's hardly a binge. Just a slip, we all make them, and now you've told us you can put it behind you and carry on with the diet. I hope it doesn't affect your ketosis.
If we are honest I think most of us have had the odd guilty nibble, and some much worse than that. But so long as it doesn't make you give up it is not a problem, particularly if it makes you more determined to carry on without cheats.
You've lost brilliantly so far and I'm sure you'll continue.