Of course, with something as important as organizing an Event, you have the option to walk back on what you posted, or cancel it completely.
To edit or cancel an event you can either press the three dots at the top right corner of the post on the timeline, or go to the event page, select the event and click the three dots in the top right corner of the cover of your selection.
Editing an event is only possible before the event actually occurs, while you are able to go back and disable an event even after it happened.