It's an unvalidated theory that the universe as a shape. A lot of popular science magazines focus on the idea that the universe could be spherical or whatnot to gain publicity. The current accepted the universe is just a 3-dimensional expanse of space.

The universe is expanding at faster than the speed of light, something to do with the Hubble constant over 70, I don't remember exactly, so unless you travel faster than light, you won't reach the edge of the universe.