Thank you for posting your query at DoctorSpring.com
I understand your concern.
I need to know more about your cycle details. But the good thing is even if fertilization occurs there is no chance of any spotting the day after. Breakthrough bleeding after fertilization can occur but takes 7-8 days. When was your LMP? There is a possibility that if you're in the middle of your cycle and ovulation occured the day before, then there can be spotting and that puts you at a slight chance of pregnancy.
So kindly let me know your LMP and your cycle duration and i can give you a more conclusive picture.
Hope this was helpful,