The exact shape of the universe is still a matter of debate among scientists. The shape can be described by the critical density.
If the density of the universe is more than the critical density, then the universe is closed and curved like a sphere.
If the density of the universe is less than the critical density, then the shape of the universe is curved like a saddle but if the density of the universe is equal to the critical density, then the universe is shaped like a flat piece of paper.
