Thank you for reaching out to us.
Based on your description, that the only sensation you felt was wetness on a leg and the only thing that you saw was on the stone bathroom floor, you are not considered niddah.
Stone (and flooring in general) is considered a surface that is not susceptible to ritual impurity, so stains on it do not make a woman niddah. Learn more here.
As a precaution against a flow beginning during relations, we usually advise refraining from relations for a day or so after non-niddah staining. This is a recommendation and not a halachic requirement.
Please let us know if we can be of further assistance.