Ask the Venue! Because you signed a legal agreement to hold your event, you may be held to this agreement by the Venue. If you need to cancel your event after the venue has already accepted it, you must contact the Venue directly. The cancellation will be handled according to the Venue’s event policy, which is stated on their ExpressBook Experience page.
Always refer to this Experience page if you have any specific questions. A simpler way to book your event comes with simpler terms, but you will have to alert the Venue to your need to cancel.