Please help... Made a new listing and instant booking was on automatically. Accepted a guest I didn't want!

In my home I had rented individual rooms. In the listings I made sure to turn instant booking off. This has been going on for 8 months until I decided to make a new listing for the entire house.

I made the listing and instant book was on by default, forgot to change it. And it accepted someone's request which I wouldn't have otherwise accepted.

What do I do now to drop this guest without being penalized!