Furless

@Furless No problem :-)

@fauxpunker Many thanks, again, for you diligence in finding a solution to my dilemma. Your explanation is fine, truly. Now, when I get a chance I shall look into it. I very much appreciate your assistance. :-)

OK, so I've been updated. To give it the little "completed check mark", you just have to make a story group and put the desired story in it. Now, creating a group doesn't mean you have to actually have more than one thing it. Once I was given my refresher, I found that the stories I have marked as complete are essentially story groups with only one chapter. Once the group has been created, you get the manage option. 
          
          That was probably a horrible explanation. This may be more helpful. http://support.wattpad.com/entries/21765506-how-do-story-groups-work

@MyztikalTearz No problem - thank you for all your help and for sharing your knowledge! :-)

@Furless If you choose to change the rating, you may have to click Contact us and submit a ticket to have wattpad change the ratings. You can include a list of all of your works in a single "email/ticket". I think there's the option to rate "up" but not to rate "down".  Sorry. I get confused about that. 
          
          Btw, Margaret Atwood recently joined wattpad :) 

@MyztikalTearz I forgot to mention, no where could I find an option to rate my work as "G" - only [PG], [PG-13] and [R] were offered. Very curious...

@fauxpunker Many thanks, Fauxpunker! Glad to know I am not the only person experiencing this. That is truly a relief.

@Furless Howdy! MyztikalTears summoned me. So, I checked my short stories and noticed the same thing with the "completed" function. However, all my "chaptered" works still have the option. I'm thinking during an update, WP got rid of the option for works that aren't grouped into a larger body. Some of my (much) older shorts still have the "manage" button, which leads me to believe that it happened in an update along the way. I'll check with some folks and see what I can find out.

@MyztikalTearz Thanks for the instructions - try as I might, I could find no "manage" link or button. There is: "new part" "edit" "delete story" and "new story". When I go to the "edit" link, I still cannot find a manage button. Perhaps the problem lies in the browser I'm using - very frustrating.
          
          Anyway, thanks on the good luck wishes with my 6th novel. And for the other good information you shared! I appreciate that you took the time to offer up some suggestions and express your thoughts.

Wattpad has come a long way in the three years since you posted!
          Here are the instructions:
          
          First, open the drop down menu at the top where it says 'Hi *yourname*' and select 'my works'. Find your story and click the 'manage' button. There should be an option to mark a book as completed.
          
          Good luck with your 6th novel!
          
          On that thought, have you considered linking wattpad to your website? 
          
          Click My Profile (shows up if you hover the mouse over your user name/profile picture).
          Click Edit
          add the url links to applicable sites - 
          website
          facebook
          tunblr
          twittr
          smashwords
          
          :)  This will be a great way to direct your readers/fans to how to locate your other works! You can certainly change your user name to your published author name, if you would like.
          
          Please let me know if there is anything you need :) 
          
          *Myztikal*