Home pregnancy tests.. ahh yes.. In australia there's a brand that is exactly the same that the docs use.. comes in a little blue box, 9 bucks for a set of two I think.
But don't worry about it mate. Had many a scare in my time with my girl. Wasn't anything to worry about. Be worried if you KNOW that the condom broke when you were having sex. And if your girl starts to worry about it. This is what got me and my girl is STRESS! This can have bad affects on the ol' period. Can make it 'dissappear' for a month or two...
But if it's not in by the next time it's due.. goe and buy yourself a test kit
That will tell you if she is or she isn't.