If you didn't want to become pregnant, then YEP, you should worry. A lot.
If it has been less than 72 hours since you had sex, then you can go to a pharmacy and get Plan-B. Though, since you were supposedly a day before ovulation, that might not work since Plan-B prevents ovulation... and it may be too late.
All you can do right now is take Plan-B if you are under 72 since unprotected sex. If not, then you are just going to have to wait until your period and then test, especially if your period is late or light. You CAN get a period and still be pregnant. My mother was 3-4 months pregnant in college once and didn't even know it because she kept having a period. She aborted, but that's not the point.