How do I stop repeating the invented story of how my partner and I met?

A friend asked what book we'd both been looking for when we met. I mumbled something about a novel and changed the subject. My partner and I actually met through a dating app. Months ago, she had joked that a bookshop sounded more romantic, and I went along when she told the story at dinner.

Now it has become the version people repeat. I don't mind keeping parts of our relationship private, but this isn't just leaving something out. We are supplying details about an afternoon that never happened, and I'm uncomfortable adding more whenever someone asks.

My partner says correcting it would make a harmless story look like a big deception. I think continuing makes the correction harder. I also recognise that I helped it become established, rather than saying something when it first came up.

How would you retire the story without humiliating her or claiming I was an unwilling participant? I would like the next conversation about how we met to be one I don't have to rehearse.