Making circles is a tricky thing in tapestry weaving. To weave a circle we believe is round, you have to trick the eye or make it really big. Tapestry is woven on a grid and to make a form perfectly circular means you basically take a square and cut the corners off. If your tapestry is huge, then this illusion is not as hard to make, though it IS still quite difficult to make a perfectly round circle given fiber’s propensity to squish and move about.
If your circles are small, it is all the harder because you don’t have very many warps to convince us that what is a shape with steps is really round.