Is there any chance that i could be pregnant?

On I think it was either the 14th or 15th of june, me and my boyfriend had sex. I've been with him for 2 years and I'm 17 years old. I don't have birth control but we did use a condom. We did it during the week that I'm supposed to be "highest in fertility", dumb choice I know. So when he was putting the condom on, he accidentally put it on backwards and it already had touched the tip of his penis and then put it back on the right side up. I'm worrying because sometimes guys can have precum on the head of their penis and not even know it. I keep worrying and freaking out that I'm pregnant because my boobs are tender and I'm showing some of the signs of "early pregnancy" but that might just because I'm supposed to start my period in 5 days. Please no rude comments.