How effective is plan b

Hi guys, I’m currently freaking out. My period was supposed to start today but hasn’t came. The condom broke and my boyfriend didn’t realize it did and he came in me. After realizing it was broken and that he had just finished in me he right away he went to buy Plan B and I took it! But my fertile window had just ended the day before. Should I be worried? What should I do? We’re both 21 and aren’t ready for kids!