"I had already read the book yesterday."
Translation:Mi jam estis leginta la libron hieraŭ.
I just picked the right answer and it says it was wrong and this has happened to me many times before...... should I report it?
Certainly. If you ever believe that you are right and/or Duo isn't, then please report it. It's one of the best ways they have of knowing where problems are in the database.