1) Change the background color for the sources on the left:  
This gray is a different color than is shown in the mockup.
Mockup color is: #E6ECF1 
Comment 2 here: https://projects.invisionapp.com/d/main#/console/14689412/333902372/comments/107550511 
2) Remove the Card from the left navigation sources. 
The "Card" is what makes a white background surrounding the source and the children. Removing that will allow for more space in the left navigation being used for locations instead of white space.