What is it anchored to? If you want it to be anchored to the edge of the screen, you need to anchor it as such. Simply turning on anchoring doesn't mean that it will be anchored to the side.
Also... make sure that both your Game View and the Scene Views are visible at the same time. If your game view is hidden behind your scene view, Unity doesn't offer any way of determining the size of it properly, so the GUI layout is not going to be correct.