Secondhand kei-car purchase, I might have been scammed

Just over a week ago I posted here asking about secondhand kei-car purchase process. Since the post, I had paid the money (10 days ago) but so far there had been no progress. I asked if they need any paperwork from my side, they said not say the moment and they will let me know.

I'm starting to get worried was I think they will need at least my juminhyo for car registration.

Do you think I have have been scammed? For kei-car purchase, do they need my juminhyo? Am I overthinking?

by hevene