Hi, it might be my eyesight that needs adjusting, but the two different background on your theme doesn't have enough contrast in the list of episodes, and the watched icon is aaall the way on the other side.
I suggest when an episode is marked, make the whole row a shade darker grey. This way when scrolling down, it just couldn't be easier to spot the place where you need to click the "watched" icon.
..or move the "watched" column next to "airdate" would also work. :)