Chance of Pregnany?

I need advice/help. I’m 15 and had unprotected sex with my boyfriend 5 days ago using the pull out method. I didn’t really want to use it and would’ve much preferred to have had a condom to prevent even the worrying of being pregnant. However, he came on the outside of my vagina, not inside, and I felt it everywhere. I went straight to the toilet but realised even if I did that it wouldn’t help. 3 days after I’ve had a brown coloured discharge or bleeding and I’ve read things about implantation bleeding. My period is due in 5 days, making it 10 days after the sex, and I’m so anxious it won’t come. I don’t have a very strong relationship with my mum, hardly even have one so I can’t go to anyone for advice. The fact I’m 15 and have the chance of even being pregnant makes me angry at myself and so so so worried.