Contemplating the Universe in a big tent in Keswick

I was sat in this big tent in Keswick and was thinking that the Universe is actually a surface like the walls of the tent. However, the tent is a 2D surface inside a 3D world. String theory suggests that the Universe might be an 11D surface but not inside anything. So when the Universe expands, it is not expanding into anything. That takes some thinking about. And if the Universe is a surface, we must be on the edge of the Universe. A surface has no inside.