Unfortunately there is ALWAYS a chance when it comes to unprotected sex. You should have thought about this BEFORE you had sex. The only solutions left are
1) Plan B pill (works UP TO 5 days after unprotected sex)
2) Abortion (where allowed - but this should be the last option)
3) Adoption (give up the kid for adoption
4) See a doctor and ask for his opinion
5) Talk to your parents - they might have some advice and help support you (in some sort of way :3)
Statistically you have a 25% chance of getting pregnant. And the fact that you had your period - well it might lower that percentage - BUT there have been cases where women do get pregnant even after their period. Yes very rare cases, but true.
Just relax, and think about what you can do if you are pregnant - make a plan and tell yourself "If i am pregnant wats next?" When you think about what you would do next it helps you calm down - and helps you prepare in case you are.
Hope this helps :3 and good luck!