Does it extend infinitely?
We can go around the earth forever but can not find the end. Likewise, the universe may be finite but endless.
Let's consider a mathematical model suitable for such a space.
A summary of Euclidean geometry is as follows:
A space is composed of a set of points and the relationship between them. The point is a location in space. Between two points, there are infinitely many other points. A line is a set of points in a specific direction at a particular point in space. A plane is a set of points in all directions normal to a specific direction at a particular point in space.
The dimension of a space is the number of independent coordinates needed to locate a point in the space. The n-sphere is a set of points at a specified distance from a particular point in (n+1)-dimensional space. The n-ball is a set of points whose distance from a particular point is less than a specified length in n-dimensional space.
