Someone please help me

I’m almost 17, I just got off my period and my boyfriend came inside me on the last day of my period and day before yesterday. And my ovulation starts in 5 days. So, I need to know if the whole “a sperm can live inside you for 3-5 days” is true or if it’s a myth because my boyfriend is freaking out and kind of making me feel like crap because if I did end up pregnant, I’m perfectly fine with it.