I accidentally hit a parked car's side mirror and it is loose/dangling off now.. (CA)

I was driving home and on a narrow street, my side mirror accidentally hit a parked car's side mirror and broke it, and it's dangling off. The thing is, I didn't notice if I did actually hit it or if it was already like that, I only noticed because I looked at their car after the fact and saw the damage. There's no damage on my car/side mirror at all. I wrote a note with my name and phone number, saying that I'm not sure if I actually hit or not, but that they can contact me anyway. I'm a college student and a new driver, I wasn't actually even driving my car, I was borrowing my boyfriend's car just to drive home, so I didn't put down any insurance info. This is the first time I've ever gotten into a car accident, and at the same time, I genuinely don't even know if I'm liable or not. I don't know if I did the right thing but I really don't want to get in trouble with the law, I would way rather pay them however much they need to get it repaired. It's been a few hours and they still have not contacted me so I'm super stressed and worried on what to do.

Location: SF