What Are The Chances Of Pregnancy Through First Intercourse?

I'm currently sixteen and had sex for the very first time. Sadly, I made the mistake of having unprotected sex and I am not financially ready for a child. I am awfully nervous and scared of being pregnant. It is my paranoia. But here is the thing, I had sex for about literally ten to fifteen seconds. Since it was my first time my partner did not go fully inside of me. We were also having oral sex before this incident happened. I really want an honest answer and some help so that I am no longer quite as nervous as I am right now. I haven't missed my period either. I am supposed to get it in the beginning of april and having to wait for my period is quite a scare. Could I possibly be pregnant? Is it a low chance? This constant worrying in my head is quite unhealthy and is giving me stress to the point where I'm constantly thinking about it when I'm not distracted by lifes everyday obstacles.