Don't worry, if you confirm after the sexy activity she have 月經 in two days later it will be fine and safety. The reason for woman to have baay is having sexy activity between the period of 2 nd and 3rd week of 月經.
May be both of you are so worry and cause the dealy of 月經 for this month.
Suggest if you would like to have sexy activity in the future please consider to use condom.