I think your chances of pregnancy are extremely low. If the condom would have broken at the tip then there could be a chance, but it broke at the top.
If you're really worried you have one more day to use Plan B. It needs to be taken within 72 hours to be effective. You can buy the pills at any drug store, and even Walmart. Just a suggestion.
I know this won't be easy but try not to stress. If you do it can delay your period. And if you do choose Plan B it can make your period late, early, or it might not come at all this month.
Another suggestion. Since you and your boyfriend are having sex you might want to think about going to your Dr or a women's clinic to get on birth control. There several options to choose from.
You're very welcome. As long as the condom didn't tear at or around the tip then no sperm escaped.
Please think about what I said about getting your girlfriend on birth control. Condoms are great birth control when used every time but as you found out, they can break sometimes.