You can hide the "Retake" and "Exit" buttons on the iPad so your guests aren't able to see them and then tap on them during the event. 

Step 1 -  Select your specific event and go to the section titled "App Experience" and select "Edit".

Step 2 - Now you can tick the boxes under "Retake" and "Exit" to hide those buttons on the app. 

Now that the buttons are hidden, you will still be able to exit the event as we have created a "hot zone" where the EXIT button normally is. All you have to do is triple-tap the top left of the screen where the exit button would have been and you will still be able to exit the event.