Charged with intention of committing DUI

I was recently arrested for DUI a few days ago while sitting in my parked vehicle. I had left the bar, walked to my vehicle, got in and was in the process of texting my girlfriend to come pick me up when a cop knocked on my window and asked me to exit the vehicle on the grounds that she thought I was getting set to pass out in the car. The keys were not in the ignition and I had only been in the car approximately 20 seconds. I declined to participate in a field sobriety test or take a breathalyzer, instead I simply admitting I was drunk and explained that I had been calling for a ride after which I was arrested. This is technically my second DUI and I’m concerned. What are my chances of fighting this?