Can I fight a DUI while parked on the side of the road with keys on the ignition?

I was drinking with my friend's dad and drove off after a while to pick up my sister I never drank any beers and I don't like drinking beer are alcohol fortunately my dad called me that I had to pick up my sister from school but didn't go far so I parked alongside the road and rested a little turned off the engine but stood there, people saw me there and called the police after they test me for alcohol and didn't pass they arrested me.