Beyond The Gates by Erin R. Howard

Death awaits outside of the Gates.

If playing by the rules means it keeps you alive, then seventeen-year-old Renna James should know better. She is, after all, the one who broadcasts these rules to the Outpost. What lies beyond the gates had always lured her, but her venture outside wasn’t supposed to leave her locked out. Now, Renna’s one chance to survive the next seventy-two hours just ran into the forest she’s forbidden to enter.