It's not "okay", no. It is not going to hurt you, but it's something you really do want to try to avoid in future. So that means it's not an "okay" thing.
Will you be "okay" every single day for the entire rest of your life? No. You'll make mistakes, you'll get busy, you'll have emotional outbursts leading to binges, etc. We all do. Those things aren't "okay" - they're bad. But when we do them, we should just carry on from there, not try to beat ourselves up.
So it's "okay" in terms of "don't fret over it" but it's definitely not "okay" as in "yeah sure, do this now and then, it's no problem". It IS a problem, and you should always endeavour to plot your day so this problem doesn't come up again.
As for today, no don't eat cake (or other) just to make up the numbers. You might find you're a little hungrier than 1550 allows for tomorrow, and that's fine - on average on the two days you'd still be below range. So if you fancy a bit more tomorrow, that's okay.
Deb, in New Zealand