Seriously though, as an architect I have to think of these things. Looks like it has only one door, understandable with the hill and all. 400 sq. ft. is kind of pushing it for something with only one door.
You should think about what it would take to get out fast if there's a fire and it blocks your way out. Like an easy open window which you can jump out of.
I'm pretty impressed that you built it yourself. I can remodel a room, but a freestanding structure, I'd probably order one online.
Bill