Stuck in Boss Arena on T5 Rare Map and Can't Complete Map

As title states I am in a Boss Arena as part of a T5 Rare Map. I teleported out to my hideout to get rid of some loot and when I cam back there was a door as seen in the picture that will not let me go through it. I have no way to complete the map now.

https://imgur.com/qdKvs7C