I worked for Motor Trend for more than ten years, and our best technical driver, Mac DeMere used to give this suggestion when drivers complained about both a lack of braking and unintended acceleration: "If your car is accelerating instead of braking, lift up your foot, and press down on the OTHER brake pedal."
Mac had extensive experience as an instructor for several racing schools and was a driving coach for numerous racers and test engineers. He competed in NASCAR’s Southwest Tour and IMSA’s Rolex 24 at Daytona. He co-drove to five wins in 24 hour races and scored several other victories on road racing circuits, oval tracks, and autocross courses. I trust his automotive advice.
I would suggest that you ensure your floormat is not obstructing the gas pedal. (I'm sure your dealership would have ruled this out.) And then take a few moments to familiarize yourself with the locations of the brake and gas pedals to ensure you're not accidentally stepping on the wrong one.