possiblility of pregnancy

I have been using the birth control patch for 6 months. During aug I had to take antibiotics for a vaginal bacteria, so I took it for a week while my period was on. Period came off that Monday before putting the 1st patch on out of the three Tuesday. Three days after that I had sex with my boyfriend that Saturday unprotected. I change for my 2nd patch this coming Tuesday. Should I be worried about being pregnant? Should I take the plan B?