Definitely a smart move to never take that exit again. Perhaps the monster pulled you into a dimension where the world was looped? Just going around in a circle forever, or possibly having two portals that you went through to go back to the beginning.

If this happens again, I’d be interested to see what happens if you instead went backwards. It could bring you back to our world, or continue going in the loop. I’m not suggesting this, but if you got stuck again I’d be curious. Also if you didn’t have the radio in your car, I wonder how the monster would tell you to take the exit? Possibly through your phone?