@Mike2293
If you cancel, you face penalties. One of them is: those dates are locked for other bookings.
If you are a new host, better do not use Instant Book and test your listing (using the price calculator or simulate bookings on your own listings) to check if everything is setup OK.
You can call Airbnb and ask them to cancel penalty free, but i doubt if the are willing to do this just because you "made a mistake".
Of all options the best is: accept the loss, learn from it, and leave the reservation in place.