@Sanna1 - this is indeed frustrating but it can be resolved easily.
First of all, with Instant Book turned on, the guest can book without any action on your part. By having IB turned on, you are automatically giving approval to anyone who requests that meets your criteria as a guest. Second, your cancellation policy is set to Strict. This means that you are entitled to 100% of the guest's booking since they did not make the cancellation deadline. https://www.airbnb.com/home/cancellation_policies#strict
However, they may qualifiy for an Extenutating Circumstances exception if they can provide support for having to leave early because of severe illness.
https://www.airbnb.com/help/article/1320/what-is-airbnb-s-extenuating-circumstances-policy
Third, if they don't cancel, you will receive the funds for the booking and not have to actually host anyone. Think of it as free money.
https://www.airbnb.com/help/article/309/what-if-my-guest-doesn-t-show-up-for-their-reservation
Hopefully this eases your mind knowing that all your work is going to result in some sort of payment. Let us know what happens with the payment issue.
For the future, if you don't want same-day bookings, you can adjust your calendar settings to require notice. There are several options. Please note: do not check the box underneath that says "Instant book...." This bypasses the notice qualification and allows same day bookings.
Good luck!