Yes I need to add a default setting button to fluid synth and FAQ about this. Just delete the config file called "Piano Booster.ini" on windows it is in "\Users\<your user name>\AppData\Roaming\PianoBooster\Piano Booster.ini" and linux it is in "/home/<your user name>/.config/PianoBooster/Piano Booster.ini"
I am glad you are a enjoying using Piano Booster. My main instrument is the flute and whistle rather than the piano. Please post back if that fixes it.