Looks correct to me (although the rest of the cable isn’t shown in the picture).
Keep in mind that even if you plug in the extension board, you still need to manually select the number of stations. Go to Edit Options -> Station Handling, and select the total number of stations. The reason for the manual selection is that OpenSprinkler allows ‘virtual’ stations, such as RF and remote stations, which are stations that are physically located elsewhere. As such you can specify the number of ‘logic’ stations that’s different from the actual number of physical stations. If you don’t select the number of stations, it will default to 8 and hence it won’t show you any station on the expansion board.