Ok, well basically, me and my girlfriend were fooling around on Friday night, and I never got my penis in (as it never got erect enough) and we were basically dry-humping with a condom on, but at a certain point the condom came off and we continued. Now, we have been freaking out a little over the possiblity of getting pregnant on pre-cum.

On the Am I Pregnant? forum, they said that I shouldn't have too much to worry about, and it's possible that she could've gotten pregnant, but it's pretty unlikely (especially if I never penetrated her vagina).

Okay, but anyway, she's been feeling sick and whatnot, and her period is coming up also, but tomorrow, she's gonna get emergency contraception, just in case, I guess to take it.

Now, would taking emergency contraception pretty much eliminate the change of a pregnancy?
Also, getting it tomorrow would be just under 72 hours, so what significance is that?