Playing the DLG mission, main menu board 50/50. How do I leave. I beat the Big Man several times and killed all the zombies it said. Mission complete but keep making me play the same board. It said Oh my god, He huge. Destroy him and leave for hood

Play the DLG mission, main menu Board 50/50 how do I leave. I beat Big Man several times and killed all the zombies. It's say mission complete but I have to keep playing the same board. Under it it said, Oh my God he's huge destroy him then leave the for good. How do I leave?