@Ann-Heidi0 Do you have Instant Book turned on?
If Instant Book is turned on, I believe you can cancel a few bookings without penalty, but call Airbnb to make sure.
If it isn’t turned on and you seem to have an unintended booking, call Airbnb and tell them you are brand new, and walk them through the steps you performed to block the days. They may be able to cancel the booking without penalty. Also ask them to show you how to turn Instant Book off, since it sounds like this is what you would like (it’s a smart thing to do when you are just starting out anyway).