Hello,
Looks like your biggest obstacle right now is your exam endurance. I have a few tips for you
1. Eliminate any distractions when doing the mock exam (noise, kid, etc).
2. Take a break (even closing your eyes for 10 seconds helps) anytime you feel that you cannot concentrate, you will notice you need less breaks as your endurance builds up.
3. Stay stress free, finish all your day tasks before starting the exam, so that you can 100% concentrate on the questions.
4. Do all 8 of the mock exams (and more, if you can) to get a good understanding of where your knowledge level is. Also helps building your endurance.
Cheers, and have a great weekend
Joe