help??

First time I had sex was yesterday unprotected. Don't wanna get too detailed but I am in need of some help. ASAP. 
I made him stop half way through and cum on his own. He was not about to cum and it was not a pull out. He just pulled out and jerked the rest off. 
What are my actual chances of getting pregnant here? Please help me. 
Should I take after pill?
I'm already on birth control. Low lo estrin. I'm 17.