Have a warm welcome and cool that you're starting to play!
I'm much of a beginner myself really so I can only give you as much advice that I learned from others..
First of all, I haven't gotten that far in the book yet, but listening is really important, though your scores decreasing in percentage by the time you progress in the book makes sense.
The lessons are designed to work up your level gradually, learning is going gradually aswell... don't mind that. It's looking good so far
If you feel like you are ready to proceed, just proceed. But if you're noticing you're having any complications because you moved onto the next stage, just take a step back and practise some more from the earlier stages, or take it slowly in the new stage. I personally don't think it's bad to look at higher level stages when you're still beginner.
For me it's motivating to listen and watch those lessons, knowing that I am not ready for them. It drives me to work on those things I find boring or that seem too repetitive. It also gives me a hint of why I have to learn other skills first if the material is too difficult, whenever I am that stubborn to still try them out.
Overall, keep on repeating the previous stages/exercises and playing songs from there, it will help you improve so I'd recommend to not stop doing them!! (even if they seem too easy for you)
Transcribing songs is also very good for your aural skills, you might want to look up that section on the site aswell. Might help you improve double time!http://www.justinguitar.com/en/TR-000-Transcribing.php
Hope this helps you making your mind up.
Best of luck!