At the beginning of the game there is a message that will recommend you to shake your mouse (or move your finger over the track-pad) very fast, and the game will scale down your input device’s sensitivity automatically. Have you tried that?
If that is not enough, you can still go into options and tweak that a bit (what is already autodetected). Unfortunately there was a bug in the demo you downloaded that locked the mouse sensitivity slider in Options, but I have uploaded now a new demo (I’m new to all this self-publishing things )