I added two nodes that were supposed to be two separate features at Navajo National Monument (36.681213835982, -110.5430872789) in northeast Arizona, and ended up with a line between the two. How do I get rid of it and prevent it from happening in the future?

I notice that Arlington, Virginia, is not identified on the map, despite being one of the most important entities in the Washington, D.C. area.
Adjacent communities, such as Falls Church, Alexandria and Vienna are called out, but Arlington, the community directly across the Potomac from Washington, is not.
The problem is, I'm new, and I don't know yet how to add a label for Arlington. Can someone help?
Many thanks.