I made my interior space first, and when I was finished, I picked a spot in the world to put my entrance and set it to teleport to the interior. When I went in the interior to do the vice versa, I selected to choose from render view (which is what I read to do) and it didn't put in the proper value, so I went to load up my other space (exterior) and I can't find it for the life of me. The world is too big to even stab at some guesses. Is there an easy way to find a misplaced object for an idiot?
I tried selecting the exteriors and searching a particular mesh or item I placed, but i'm having no luck at all.
I'd go with the SkyEdit suggestion, but if you don't want to do that, and if you haven't been moving stuff around, you could look for the asterisk next to the cell, which would tell you something was edited in that cell. So, if you put your door in the Tamriel world space, go to World Space, select Tamriel, then scroll down through the editor ID in the left. Any cell in which you changed something will have an asterisk to the right.
and as an FYI, once you check the teleport from one door to the other, you do not need to do it again. Just make sure the yellow markers are placed correctly next to both doors and pointing in the right direction.