Hello, I have gone through your query and understood the concern. Ovulation occurs two weeks prior to the onset of the next cycle. Going by this, you had the intercourse during the safe period. You may have conceived during an earlier act. In rare cases, when there is a defective corpus luteum function, the post-ovulatory phase is shortened. Then, the cycle becomes shorter and conception can occur even a week before the next cycle. Please see a specialist, get a clinical confirmation followed by a sonogram of the pelvis preferably in the trans-vaginal route to know the age and the location of the pregnancy. If you do not wish to retain it, you can ask for an abortion. Hope this helps.