What Are The Chances Of Pregnancy After Non Penetrative Sex?

I am 18 years old and really need help. I am in a long distance relationship with my boyfriend and he came down in December. We really love each other and we are very clingy. One night, things got a little heated and were laying down with my back facing him. He started to rub his ... against my vagina but he never went in. There was no penetration. However, I am absolutely terrified I might be pregnant from the possible pre-***. He hadn't ejaculated in 2 weeks when that happened. Please help me. I'm scared!