No, the earth is not a perfect sphere. It’s actually squashed in a bit at the poles, and widest at the equator.
The diameter of the earth, an imaginary line drawn through the center of the earth from one side to the other, is about 7,926 miles at the equator, but only about 7,900 miles from pole to pole. The earth is more than 26 miles wider at the equator than it is at the poles!
The term that mathematicians would use to describe the shape of the earth is oblate spheroid.
The earth actually has four corners, points where the surface of the earth bulges slightly. These corners are in Ireland, and in the oceans near Peru, South Africa, and New Guinea!