Walking around downtown Leesburg is always a fun way to kill a few hours. Check out the lines of shops, cafes, and restaurants. Shoe Cup & Cork is a favorite spot (go through the alley to their "secret garden" complete with bocce ball). The book store is also a fun place spend time.
If you're looking to shop, the Leesburg Outlets has premium options - and it's massive, so there's something for everyone.
If you have extra time in the area, the National Mall and all its museums and monuments are only about a 45 minute drive away! You can Uber or take the silver metro line from Ashburn.