It’s a 3D shape, so it would be a sphere, rather than a circle, but it’s not quite that regular!
Because of the rotation of the earth, the ground in the middle at the equator gets pushed out, and it gets squashed down at the top and bottom, at the poles. The diameter of the Earth top to bottom is 25 miles less than at the equator!
This kind of shape is called an ‘oblate spheroid’ and it looks like a slightly squashed ball
Well, the Earth always looks like a circle from the outside, wherever you (until you got far enough away that it was a point).
In fact, people in ancient Greece knew the Earth was a sphere – they could see the shadow on the moon and since it was always circular, they realised the Earth must be a sphere, since a sphere is the only shape to always have a circular shadow.
Like Leila says, it’s not perfectly spherical, but only very slightly. If you were to make a snooker ball the size of the Earth, the Earth would be smoother and more spherical than the ball.