@Sharouq0
You are on Instant Book, to turn it off:
https://www.airbnb.com/help/article/1510/how-do-i-turn-instant-book-on-or-off
You can contact Airbnb and explain you made a mistake, maybe they are willing to cancel penalty free.
Contact Airbnb - Community Guide [Updated]
But it is your responsibility to have your listing settings and calender availibility in good order. The guest can not be punished for this. BTW The guest can cancel with full refund within 48 hours after booking, according what's stated in your listing under "cancellations". But you and guest should read all conditions first.
Best regards,
Emiel