Good deed and bad karma

In Baltimore for a meeting, which has meant long drives and long hours for the past 4 days. Today, I am coming home relatively early and I'm happy to have "escaped". At the last light before the beginning of the highway I see a man coming to my car with a small cardboard that reads "Homeless. Please help". I honk , open my wallet and my window to give him money. The light has just turned green and the car behind is getting nervous honking to get me moving faster. I start and get on the highway, feeling good to have helped him even if only with a dollar.

Only back in DC that I realized that I had given him a $10 bill instead of the intended $1.
Now I am annoyed at myself to not having looked more carefully. No more of feel good and just thoughts about checking more carefully next time.
Doing and feeling good on the cheap.