Are the practice exams feedback based? If not it may be that the school is pushing you very hard now so that the exams appear easy. If they are feedback based, use each exam as a lesson. Do every question then find out what you got wrong and why. Then do it again immediately. And again. It will work I promise.
Didn't go full time so don't know if you have a brush up course. If not and you are still doing badly then go to Bristol for one. They are excellent.
But hopefully you won't need it.
Good luck
SK