Gauge / Chart update Problem

First delete all the widgets from the dashboard, then make the below changes into your code and upload it. this will populate your dashboard with widget, add them.

int p;
CAYENNE_OUT_DEFAULT()
{
  Cayenne.virtualWrite(0, millis());
  Cayenne.virtualWrite(1, bme.readTemperature(), "temp", "c");
  P = bme.readPressure() / 100.0F;
  Cayenne.virtualWrite(2, P, "bp", "pa");
  Cayenne.virtualWrite(3, bme.readHumidity(), "rel_hum", "p");

}

Have a look at this Data types for Cayenne MQTT API