Change Icon Size in Unity 2D Launcher [duplicate]
At this moment, here is no way to change the launcher width in Unity 2D, as you can read here:
https://answers.launchpad.net/unity-2d/+question/158873
https://answers.launchpad.net/unity-2d/+question/141757
I suggest to register to this bug on launchpad, that is the related feature request:
https://bugs.launchpad.net/unity-2d/+bug/789638
Note: the are few other options you can choose, see question How do I configure Unity 2D?