I had the same feeling as you few months ago. The first 4 of my mock exams are 59% 55% 51% 53%.
First of all, if possible, you can reschedule your exam before the 30-day mark. That would automatically take away some stress off you.
Secondly, you said you read through the PMBOK but scored badly on the exam. One of the reason is because you didn't remember the concepts, you only recognize them as you read through
Strongly recommend you order the Rita book. Use the triangulation method (ex. For a specific chapter, read PMBOK+Prepcast first, then the same chapter in Rita's, finally pick off the really hard concept by watching a visual demo like Youtube). I guarantee you will significantly increase your next mock exam score using this method (for me, my 5th exam was in the 75% range)
For the first few mock exam, review ALL questions even the correct ones. Do as much mock exam as possible (PMzest, Prepcast, OliverLehmann etc etc). Jot down why you answer the question wrong (is it something you never encountered? something you don't remember? or simply just human error) and go back to that specific section in the PMBOK to review.
You are doing fine... just to give you an idea.. I have my PMP Tomorrow.
I have read the PmBook Guide
Ritas PMP Book
PMP Fast Track Video
I have done over 1500 questions.. and still my scores are not why i Want... every time i take a test.. I make sure I review the questions I got wrong and take note... ITS A FAILURE UNTILL YOU DECIDE TO QUIT... Take it easy and just focus , get extra learning aids and dont.. worry , just keep a positive attitude and put in the hours to improve.
You still have time... besides its just a test... its not a life or death issue.. so relax