I'm chuckling to myself here, Beverly, because you sound just like me having conversations with myself!

Here's the rational Beverly: you KNOW you've been on plan, you KNOW it's just water weight, not fat, you KNOW you'll get right back on plan after your planned treat, you KNOW this strategy has worked for you while you lost 185 pounds ... OK, that's your rational mind speaking and it's making lots of sense.
But then there's emotional Beverly: OMG, I've gained two pounds and now I'm going out to eat and I'll gain even more and it's all downhill from here and in a week I'll put back on all the weight. It's that old

emotional thinking.
You know which voice to listen to, right?

My advice to you is go out and enjoy your planned dinner - and I hope it's a good one!, get right back on track tomorrow (which I know you would anyway) and stay off that stupid scale for a few days to let the weight fluctuations settle down.
Remember that 60% of your body weight is water, so if you weigh 135 pounds, you're carrying around 81 pounds of water around! A two pound fluctuation is only about 2% of the total and isn't statistically significant at all. So you're holding 2% more water - not really a big deal, eh?
Honestly, I don't know if the head stuff goes away or if we ever stop having these conversations with ourselves. But I DO know that you should go and have a lovely dinner!