Is the pill 100% effective??

I'm 15, i recently visited the gynaecologist and she gave me Diane 35, my mom agreed to it because it diminishes period pain and pimples, but it also prevents pregnancy. I take the pill every single day, and not so long ago I lost my virginity with my current bf, we don't use condoms anymore but we are still scared of him cumming inside of me.. you know it's kinda scary, so what should we do about it??