How likely?

So I'm always scared that I'm pregnant ever since I've started having sex. I'm on birth control that I take on time everyday and double if I've missed a day( which was only once and we weren't intimate that day), we use a condom( sometimes two for safety ) , and he always pulls out before he finishes. How likely are the chances of me being pregnant with all these factors? I'm only 16. Not ready for parenthood.