Should I Take An I-Pill Or Continue Regestrone To Prevent Pregnancy?

I had unprotected sex on 31st March and started taking regestron from 2nd April, in between I missed taking regestron one day. I ve taken 7 tablets till now and on 9th April while having protected sex the protection broke out and my partner came inside me. I m afraid I might get pregnant, I am having very little cramps, when can I expect my periods and should I continue with regestron or should I take ipill. How to avoid pregnancy