i need some reassurance

three days ago i had unprotected sex that lasted about 5 seconds. he didn’t finish inside of me but does anyone know if there is still a chance i could be pregnant? my breasts have been really tender and i read that is an early symptom. i’m only 15 and realize having unprotected sex was extremely immature and plain stupid. any reassurance or tips you could possibly give me would me greatly appreciated :)