How to use MIDI controller like a laptop touchpad?

You can do either or both of these
a. limit the area it controls to the range of values it can produce
b. scale the values i.e Mouse.X = (Screen.Width/128) * controller.X;

Many MIDI controllers can output two lots of 7 bit values to give 14 bit CC resolution - you also get a repeat of the status byte if running status isn't used, plus the paired controller byte. This would look something like

1sssssss (status)
0ccccccc (controller LSB)
0vvvvvvv (LSB value)
1sssssss (status if no running status)
0ccccccc (controller MSB)
0vvvvvvv (MSB value)

Your controller may possibly have a setting to enable this which would give you 0 - 16383 which would be plenty!