How can I atone for being cowardly?

I panicked over a minor parking lot mistake. It was totally my fault, but due to another insurance issue, I left a note with an illegible phone number. Guilty over this, I got an envelope containing several hundred dollars. Unfortunately, by the time I returned, the other driver had seen my ersatz note and drove away. Since I cannot make this up to that individual, how do I atone for my cowardly act? I have been trying to do random acts of kindness in hopes that karma will somehow even out.