Hi @Roseanna9
This is very unfortunate!
It sounds like it was a one-night booking (Saturday only), so at least the damage is limited.
Can you see whether it was processed as just a refund, or a cancellation?
I worry that it went through as a host cancellation, which will count against you.
I doubt you'll get your money back, but it may be worth trying to argue that it at least shouldn't be recorded as a host cancellation due to the confusion.
As I think you realise, the problem was the fact that you mentioned "double booking" to the new guest - you should only have explained the situation to the original booker (who lost out, but it wasn't your fault) and let the new booking go ahead smoothly.
I can't see your calendar as your profile only says Guest (are you a co-host?), but you could check whether Saturdays are far more popular that other days, and perhaps consider a minimum weekend stay or a slightly higher price on weekends.