Opening at End of Corridor Instead of Black

Hello – this is a great project and I’m enjoying putting this corridor together. I’ve been successful so far, however, when I render, I am not getting black at the end of my corridor. The animation is looping properly, but it is only showing an opening on the other side instead of black. I keep checking the section to see if perhaps I’ve missed a step.

Please advise what I should double-check or fix to get the correct render.

Thank you.