Sooner or later somebody is going to discover that you can play the harmonica. Eventually you will be asked to play your instrument in public. While you might be reluctant to do so, I encourage you to do it. You might just be encouraging somebody in the audience to learn to play the harmonica. They may think to themselves, "If he can learn to play the harmonica, then surely I can."
I have the following suggestions when you perform in public:
1. Practice a song at least fifty times before performing it in public. This will not only improve your playing, but it will also give you confidence, something you will need.
2. Choose a song with which your audience is familiar.
3. Don't try to show off your skill. Instead, seek to communicate the message of your song. You want the audience to be thinking of the words to your song, not thinking about your awesome musical talent.
4. Use a microphone if playing in front of a large audience. Put the harmonica as close to the mike as you can, even one inch away is not too close. Play gently and let the mike amplify your volume.
5. If you goof up, just continue on playing as if nothing was wrong. They will most likely think you are improvising.
6. If at all possible, find a guitar player who will accompany you. The harmonica sounds 300% better when accompanied by a guitar or banjo. It also reduces some of the pressure on you. It is much easier playing in public as part of a band than as a solo.
7. Only play one or two songs. It is better to leave them wishing you would play more, than wishing you would quit.