@Luan14
@Rachel177 and @Ana1136 are right. The host is allowed to cancel an instant booking if he feels really uncomfortable to host certain guest because the guest has bad reviews or intend to break house rules. But in this case, you should contact Airbnb CS, explain why you feel uncomfortable and let Airbnb CS cancel it for you.
You are not the first new host who made this mistake and we agree, this information should be explained better and more clearly. Unfortunately, Airbnb likes to obscure and hide information and features which are not guest-centric.