I did my IREX last year, passed OK, but was still majorly ticked off at getting some of the basic Q's wrong
READ the questions! It's so easy to misread the Q.
CASA quite sneakily include answers for people who misread the Q's - for ALL their exams. They factor in the most probable mistakes and slap those answers in too, so don't assume anything.
Good luck. Yep, the several hour drive back lets you think all about it!