Ironical story. Read and advice

One fateful day, my dad sent me to deliver a letter to a Lecturer. He gave me a new #100 note but I also had another #100 note. On my way I dipped both the money my had given me and the letter into my back pocket, not knowing the money found its way into the sealed letter. When I was to pay for the trip, I couldn't find the money, so I paid with my own, later I reasoned that the money was with the Lecturer. How do I collect back the money? The Lecturer might be thinking my Dad bribed him with #100 note, how do I live with this?