You should have received an email from PearsonVUE after you booked the exam with various details including the cancellation policy, which can also be found here:
https://www.isc2.org/Exams/Before-Your-Exam#2dc8f11cea5e4fea933be36198630662
In summary, as soon as you have booked, if you want to cancel it will cost you $100 so you won't get a full refund.
Probably better to reschedule for $50 if you think you can prepare for the exam within the required 365 days.
