A nice story, and a fun premise. But it could use some tweaking.

For one, a few lines feel lacking, not to say they need to be fancily worded, but they could use a bit of fluffing up. Another thing is the reveal, Mina should have withheld her name until the dinner date, thus making the connection to her and Ivan a bit more surprising (at least in the context of the story).

Also, the flashback just seems to happen, and should either be done in italics to make it more clear, or be told more like a proper recollection. Here, it sounded like it was meant to be a flashback that just sort of begins suddenly.

Finally, Mina's desperation could use more build up. Like subtle hints that Ivan doesn't pick up on, until Mina reveals her plan to piss herself. It should also include more detail about how other people are reacting. Do a lot take notice, or does it go almost undetected?

Though I would say you could even toy with the option that Mina offers to wet herself as she and Ivan leave the restaurant.