unprotected sex

So last night I ended up having what I would call break up sex with my bf that I had been with for over a year. Even though he camed outside of me I am still a bit worried , I'm not planning on a pregnancy and I'm not ready for one and i know I should've been smarter. I am on my week after ovulation and even though the chance may be low I am freaking out so  What should I do? Should I buy an after pill? Or should I not worry so much ?