Incomplete intercourse and pregnancy possiblity ?

I had sex with my girl friend about two weeks ago.I didn't know that precum causes pregnancy.but i heard about that few days ago.i'm not sure about it.i tried the sexual intercourse.but when i tried to insert my penis she told me that it's painful,so that i took it out.i couldn't insert even my head fully into her vagina,because it was so tight.so we stopped it.will she become pregnant?i'm sure that no sperm was ejaculated.but precum did.but i could insert only about half of my head into her vagina.it didn't go beyond that.could she become pregnant?she says that she will kill herself if she's pregnant!please help us..she had had her last menstruation on 11th of February.please help us!!!