Is there any way..

Alright, so I'm on the pill, Minastrin 24 fe to be exact. I take my pill around the same time daily, don't miss any but might have an hour window in which I take it. Boyfriend and I had sex with no condom on the 19th day of my cycle, May 18. The day after, started having some slight cramping and breast tenderness. Did have a two day long withdrawl bleed (only four placebos and first and last were accidentally switched by bf). Took a pregnancy test a few days ago in the evening, the digital clear blue one with the weeks counter and it said not pregnant. Is there any way I could still be? Or am I worrying for nothing?