My advice is not to give up because you have already invested so much time and energy. It is best to focus on older material sometimes because those text have more foundational material and theory. If you grab hold of the theory behind the objectives you won't be upset. You will ace it the next time.
I feel for your disappointment in not passing this exam. But I sincerely think that you are being way too hard on yourself. If you took this test on March 5, 2018 then I'm miffed as to why you did not know that your CISSP exam was going to be in the CAT format.
You have to be honest with yourself and know that you probably did not prepare for this test as much as you could have or should have. Don't be dismayed at (ISC)², as they have put out and posted the information in enough time for anyone taking this exam to prepare. I also studied for the linear version, but I was made aware of the changes. However, if you were primed to pass the 250 question linear exam, then I don't see any reason why you would not have been also prepared to pass the CAT format of the exam.
Just prepare to take it again. If you need assistance, just contact me and I can assist you. But by no means do you fail an exam and blame it on the exam that you failed.
See you on the other side of this CISSP journey!