Will Tri Sprintec Be Effective If Taken From 1st Day Of Menses?

I began taking Tri Sprintec as a birth control on February 17th, the first day of my period and have taken it at the same time every day since. Yesterday (February 24th I had unprotected sex with my boyfriend and he did ejaculate inside me. The insert in my pill pack says that if Tri Sprintec is started on the first day of my period then it is immediately effective. Should I be worried about pregnancy even though it says it's immediately effective?