That was very kind of you to make sure to call the authorities to get help for the poor kitty.
I was in a similar situation: Once I was driving with some people from work in the car, and we were on this main road, and all teh sudden i saw this cat in the middle of the road. It was clearly in a lot of pain, it was breathing really labored with its chest heaving up and down. I was so upset and shaken by the sight of it. I wasn't sure if I shoudl stop and do anything, especially since I was pretty sure I saw an animal hopsital down that road. But when I looked back, I saw someone else had stopped and was trying to pick the cat up and get it help. I felt relieved that someone else had taken care of this cat (who knows if it made it or not), because I don't think I could have handled it.
Please don't feel bad, you definitely did the right thing.