If you had a regular period, you're probably not pregnant.
However some women do have bleeding during early pregnancy, sometimes around the time that their period was expected. This bleeding is often slightly lighter than a normal period, though some women may mistake it for a normal period and not realize they are pregnant.
Chances are pretty good that you're not pregnant, but if you begin having any pregnancy symptoms (nausea, vomiting, breast tenderness, bloating, frequent urination, etc.) or miss another period, definitely take a home pregnancy test. If you're really worried about it, you certainly could just take one now -- they're not too expensive, and it's a small price to pay for peace of mind.