Scared & pregnant maybe??

Okay so I don’t know what to think or how to feel at the moment. Me and my boyfriend had unprotected sex on Wednesday and that so happened to be the day before my fertile week started which I stupidly wasn’t aware of. He pulled out before he came but I still feel a little bit off because of the pre cum. I know it’s rare to get pregnant off pre cum but it’s possible and that slight possibility scares me. We’re both 18 and I don’t think I’m ready for a kid but he says he is if it comes down to it or we can explore our options. Neither of us had the money to buy a plan b either and it’s been almost 4 days and I’ve been feeling sick these past few days my stomach has been bugging me. I don’t know if I’m overthinking it too much and it’s all in my head or if this is the start of a pregnancy.