Well, you do have to follow directions when you take the morning after pill. You have to take the whole pill within 72 hours after the event for it to be effective. So, unfortunately, you took enough hormones with half the pill to make your period/cycle irregular but not enough to stop a pregnancy. The penis emits small amounts of sperm even before ejaculation so sperm was inside your vagina. Did it get you pregnant? Hopefully not but you will have to test 2.5 weeks after it happened to know for sure. Thinking it probably didn't but there is no way of knowing until then. Good luck and let us know!