There is another way to set the mouse sensitivity with a GUI program, xserver xorg input synaptics. To install it run the following command in a Terminal window.
sudo apt-get install xserver-xorg-input-synaptics
Once the program installs you can find it by searching your programs for KEYBOARD AND MOUSE. Running it bring up the following with the needed options.
This will allow you to adjust your sensitivity and acceleration along with some keyboard functions.