Hello dear I understand your concern Do not worry There is no chance of the pregnancy as you did sex on the last day of period. It is very safe period of the cycle. During this day there is no ovulation so fertilization will not occur. But if some sperm concentration enter in to the vagina during the fertile phase/ovulatory phase of cycle then chance of pregnancy is high. But you are safe. Avoid stress, take healthy diet, maintain proper pelvic hygiene, do regualr exercise. Use safe sex practice like condom in future to prevent the unwanted pregnancy. Hope this may help you Best regards Dr. Sagar