How to express surprise when you do not expect something and forced to do it

I often hear "This comes as a surprise," which has the advantage of being neutral and factual. It allows to express how you feel while not giving to the other party the feeling of an escalation.

If you feel that you have been surprised by information that you should have known about, you could say that you were blindsided by the restaurant.

Merriam-Webster, "Blindside," verb:

1 : to hit unexpectedly from or as if from the blind side // blindside the quarterback

2 : to surprise unpleasantly

Cambridge Dictionary, "Blindside":

to surprise someone, usually with harmful results

In your situation, you could say:

I understand this is a Friday night, and you must be really busy, but I feel a bit blindsided: we did not expect to have to leave so early.

More common responses expressing surprise in these circumstances cut the nonsense about understanding it is Friday night:

Well bugger that! I’ll leave when I’m good and ready and not before!

Where did you dream that one up, Jimmy? You know where you can stuff it!

or, drawing on another question on this list:

Sod that for a game of soldiers!

However, if you are in Bertie Wooster country your response can be more measured:

I say, fellow, that’s a bit steep. They don’t treat one like this at the Ritz.