I should be OK, the CCC backups are decent.
I wonder if the beta installer picked up the wrong version. When I ran it on my MacBook, I'm sure it said it was installing Big Sur but when I ran it on the iMac, it said Big Sur Beta. A friend also ran it today and his installed after a few attempts and then it offered another update to 11.0.1. My MacBook grabbed 11.0.1 straight away.
/edit - Yes, I'm back to Catalina. When I do a get info on the Big Sur install file it showed a creation date of September. That's very odd. Anyway, I won't be trying this again until the official release tomorrow.