Can Having Unprotected Sex Followed By Intake Of Unwanted Pill Avoid Pregnancy?

Hello Doctor. I had unprotected sex on 15th of march. I was unsure that my boyfriend ejaculated in me or not so i took a pill of Unwanted 72 within 28hrs. My periods last 9 days and i have a cycle of 28 days. My periods had ended on 14th of march and had sex on 15th of march. I took unwanted 72 on 16th i.e. 27hrs later. Its been 5 days now and i dont find any withdrawl bleeding. My next periods are due around 4th of april. I am very tensed now. No withdrawl bleeding till now. Please help me. What are the chances of pregnancy? Help !!