Technical issue with 4th Grade Reading and Vocabulary section

Hello I'm Chen Xi, a student who is having a tiny little issue here with the 4th Grade Reading and Vocabulary section. I simply went in and did an exercise called "The Great Invention of Hugo Cabret" and got a full score on it, but when I went out of the unit and went back in again it said that I got only 75 percent on it (which was my score before). I was then absolutely furious after trying several times only to see it say 75 percent. I don't know what to do so – if you can– please give me a solution to this problem.