Yeah don't overstress OBK, I actually don't think anyone ever feels 100% ready to do the exams and I remember having the exact same thoughts when I was trying to decide when to put in for them.
As long as you get through all the material before going for your brushup, you'll be amazed how much is crammed into the two weeks at BGS ! Put it this way, don't plan too much for your evenings whilst down there !
If you can maybe spend a week or two going over all the material again (or as much as you can) before going back to BGS as I did, that helped, but if not, don't stress as the team will go through it again. It really does bring you upto speed for the exams. Worked for me anyway on both modules.
Good luck.
