How to remove the blank space next to the price scale 

If you see a blank space next to the price scale, it is most likely that your chart has several panes. The blank space will appear in case one of the panes either uses several price scales or its price scale is located on an opposite side.

To remove the blank space, you can pin the indicator linked to it to the price scale of the main series. Just click on the three dots in the indicator line and select Pin to scale → Pin to scale A.