At this time, the Watchlist can only be sorted in the Tile view. If you would like to do additional sorting and/or filtering, switch over to the List view (read the product guide entitled How do I sort and filter my Watchlist in List view? if you need a refresher).
1. From the Tile view, click on the Watchlist sort dropdown in the top left of the screen and select from the available options.
2. Once you have selected your Watchlist sort option, your list will refresh. For example, if you select A to Z, then the list will sort the security symbols alphabetically in rows from left to right, and then top to bottom.