Android Question Why does a view not fit the whole screen in your phone?

I have added a webview in the designer and stretched it so the darkened rectangle is filled with the webview on left and right sides. However when loaded on my phone although the left side of the webview is flush with the left of the phone screen, the right side is short from the right side of the phone screen, there is a white gap between the right side of the webview and the right side of the screen.

Do I have to autoscale or something?