It's true, and we don't have a lot of sources to infer what the commoner knew. But when a scientific fact is a consensus among scholars, even if literacy is low, it finishes in the mind of the whole population. In the 13^th^ century, the roundness of Earth was a consensus for more than 1000 years... it's safe to assume that it was known by almost everyone. Moreover priests, even low profile priests, received at least a basic education, and they would know that the Earth was round, and they would spread that knowledge.