What Are The Chances Of Pregnancy Having The Precum Released In The Vagina?

Hi doctor, I'm 18 and I have been on birth control for a little over 4months now. My boyfriend and I had sex with a condom, and he always pulls out just to be safe, and it wasn't there. It got stuck inside of me, and I am a little nervous because of pre-cum. I plan on buying a morning after pill tomorrow morning, what are the chances of pregnancy?