@Katy311 There are many penalties for cancelling, your calendar being blocked for those dates being one of them. You should never do a cancellation yourself- if you have a valid reason for cancelling, contact Airbnb and ask that they cancel for you without penalties.
As to this cancellation, you could contact them, plead ignorance, that you're brand new to this and didn't understand how it all works, and see if they'll forgive this one, just this once, pretty please, and unblock the dates.