You can never cancel without the dates being blocked. If you accidently accept a booking with the wrong dates, wrong price or whatever, you will have to honor it. If you feel unsafe with the guest you can call AirBnb and have THEM cancel it and your dates will not be blocked.
They won't let you just cancel without penalty for reasons such as "made a mistake" , they only cancel without penalty for safety reasons or extenuating circumstances such as death in family, illness, plumbing not working, electrical outage, earthquakes, riots, war.
If you cancel without an extenuating circumstance you will also be penalized - Airbnb will charge you a cancellation fee. They don't want hosts cancelling. Especially after accepting a reservation at a lower price, they don't want you cancelling and asking for more money. That's a bait and switch and is unethical. They expect you to honor your commitment to the guest. The fact that the price was wrong is not the guest's fault. The guest booked at the price they saw, not at some imaginary price you expected would be in place.
If you have to cancel for safety or a crisis and don't have time to call Airbnb you can cancel yourself and try to talk to them later and see what they will do about it but it is better to contact them first if at all possible.
You might be able to persuade them to unblock the dates because you are so new, your son accepted without your permission, the dates are so far away and you are willing to accept the original guest's reservation. You could call them.
Never never cancel.
