Pregnancy scare off Pre-cum. On Alesse birth control.

Hi everyone, I am in a steady relationship with my boyfriend, both 18, and are planning on getting married after university. I have now been on Alesse birth control for 3 months, (it will be 4 months in 2 weeks). We had sex with no condoms last night BUT he did not ejaculate inside of me. I keep getting mixed answers for pre-cum and I am extremely confused. I know there was pre-cum, which is why i am worried. I am NOT ready for a baby. He pulled out before ejaculating, we went swimming in a chlorine pool before, he did pee before, took a shower and there was no previous ejaculation in the last 24 hour. So seeing these circumstances, what are my chances of being pregnant ? (oh and I take my pill everyday at the same time, maybe half an hour different time, but still always around the same time) I am extremely paranoid, any help is appreciated. Thank you !!