It depends how much you left, if it was only a mouthful or two it will make no difference. They teach you to work out your carbs and insulin injections very precisely, but human bodies just don’t work like that, you’ve actually got more wiggle room than you would expect when counting your carbs. Which is why when we eat out we very rarely bother trying to carb count accurately, we just eyeball it and take a guess - an educated one yes, but if I guess 50 for a plate of scampi and the official nutrition info for the pub says 47 then that’s neither here nor there and won’t make a significant difference to your insulin dose. If I guess 50 and it’s only 25 then I might have a problem... but we’ve been doing this for 9 years now and between us can guess most things well enough.
Added to that, you get some days when you know you’ve counted everything absolutely accurately and you still go low... there are too many things which influence blood sugars, carb counting is just one of them, as long as you’ve got it fairly accurately right then that’s all that matters.