an American story then leave it alone because there is no way you can alter the sentence patterns, choice of words etc. to make it sound Standard English and not American.
BUT
Have you checked your market out seriously. The literaries will accept an American story, but the genre mags like to have a British connection through character or setting or situation.
Obviously SF and Fantasy stories have different requirements.
Interesting take on it. I can tell you this. It's clearly an American story. The setting is a theme park. There's no UK connection at all. No getting away from that. It's also clearly genre--psychological horror, probably. Maybe suspense.
Frankly, I've checked this market out less that I would have liked to. It's a 6500 word short and there simply aren't that many places for it, based on length alone. I have no problem checking out anthologies, but my writing partner and I wanted to check out the pro markets first. We've gotten two encouraging rejections (as encouraging as a rejection can be), and want to give it this shot.
I can tell you this. As an American, I very much enjoy reading UK stories that are obviously all UK, with no American connection whatsoever. Of course I also like those with the occasional American connection.
I never expect anything when I submit, so I won't be disappointed with a rejection here. But, what the hey, it's worth a shot.