With Wrong Answer Mode, once you have studied a section you can return to it and study only the answers you have got wrong. This really helps you focus on the sections you are struggling with to help you boost your grades!
You will be able to see how many answers you got wrong at the end of each topic.
It is possible to get 100% in a session and still have some wrong answers. This is because you won't see all the questions every time you study a topic. There may be some questions you got wrong last time you studied but you didn't see them this time.