Astronomers are getting the size right
The general relativity theory allows for three different ways in which the universe could bend. The three ways allow it different characteristics and determine whether it is finite. So far, observations indicate that the universe is flat. 1 A closed universe
has a positive curvature. Two light beams that are sent off in parallel will meet at some point, and the angles of a triangle will total more than 180 degrees combined. 2 A flat universe
has no curvature. The two parallel light beams will never meet, and the total of the angles of a triangle add up to 180 degrees, as we know from 2D geometry. 3 An open universe
has a negative curvature. Over long distances, the two light beams will remove themselves from each other, and the combined angles of a triangle will be less than 180 degrees.