Hopefully you didn't take emergency contraception for this. Ejaculating on your rear end if he hadn't been in your vagina would not result in pregnancy and especially if you had panties on. This would be no risk for pregnancy!
Agreed. Even so, you should not play games like this in the five days before ovulation. Instead you can pleasure each other by hand or mouth
Remember that female sex drive is highest at ovulation, so be extra cautious around that time.
Muslim families are not tolerant of premarital sex, and your boyfriend is pushing you for his own pleasure, not because he has marriage in mind. Best to give it a break.