Hit and Run!!!!!

I live in Washington state. I was at a friend's house about to pull out of their long, dark driveway. I was the designated driver. A car was parked behind me and a bit to the right, so when I backed up and turned, I hit it. At first, the bump was so light, I thought I had hit a big rock with my tire. I drive a rav4 and I'm only 5'4", so it's hard for me to see out the back. It turns out, one of my passengers saw that it was a car. Everyone in the house was drunk and partying and I had no i