Am I pregnant?

So me and my boyfriend had unprotected sex four days ago and he stressing about me taking a pregnancy test. He pulled out but it says to take the test 21 days after doing it. The problem is that 21 day limit ends on the same day my next period should end according to eve. Should I go ahead and take the test? And also the next day after sex I found brown stringy stuff in my underwear, is that bad? It was only my third time having sex. I'm freaking out and I'm scared I'm pregnant, any advice?