Yeah, I used to do these challenges before, but sometimes they become a chore. Why not change the rules for yourself a bit, if the book becomes a drag, you can just leave it midway, and consider it done for the bingo challenge. That's what I do now, if I have have given it my best, for me it is as good as done.

Of course, if this is some kind of competition, then you should either finish it completely or don't mark that item, but these bingo cards are just for fun, and made to broaden your reading genre/author/etc, so you decide how you take them.