Help!!! Preggers???

Okay, ladies, I had unprotected sex with my S/O on January 11, which was on my week of ovulation, exactly two days before my most fertile day. Now, my cycle was suppose to began on the 27th of this month, but the app I use isn't the most accurate because my period is slightly unpredictable. I've discussed this with my man and he wants to wait before buying a test because we've thought we were pregnant before and two days later my cycle started. But...I'm terrified. Help??