I'm worried

So me and my boyfriend had sex on Valentine's Day. I'm on the Depo shot. He didn't wear a condom and he came inside me a little. I have really bad anxiety and I always worry if I will get pregnant. My first shot was on January 5th 2016. Is there any chance I will get pregnant or no since this is my first time on the shit and what exactly does it mean by "perfect use"?