Even in Geometry there is no such thing as a perfect circle. If there was we’d have found the final decimal place for Pi by now. No matter how many points are used to define a circle at any radius, it will still have its corners at every point.
A circle has four sides: inside, outside, top and bottom.
IIRC, isn’t there something about using calculus to find the limit of perimeter of a polygon as number of sides approaches infinity? It’s been many years.