Can a penis with some precum at the tip get a girl pregnant even though it only went in about an inch?and does peeing before help prevent pregnancy?

Yes: Pre-ejaculate semen contains plenty of sperm, certainly enough to get a girl pregnant. And deep penetration vs "only went in an inch" doesn't matter - it was still in the vagina. Finally, no, urinating before sex doesn't work as contraception. You and your girlfriends need to talk to a health professional about contraception and condoms, or you will be a dad before you know it.