Exams are not much about using your intelligence really. They're about recalling information, mostly, not problem solving.
IQ = problem solving
There are plenty of people that have good IQ and don't use it. Someone with 130 IQ who only uses half of it, won't do as well as someone with 95 IQ who uses all of it. Like others said here, work ethic matters a lot.
Obviously it makes life harder. IQ is not 'meaningless' like some say. If it were, then admittedly the difference between our IQ and chimpanzees would be meaningless too, which is stupid. But life success is also far more complex than being simplified down to only a matter of IQ. The friends you make, how you treat people, your personal values, what you use your IQ for, etc. All these things matter. Some people with very high IQs end up putting their potential to very bad use. That's less than useless, it is destructive. You do not need a high IQ to get a leg-up in life on people like that, you just need to be a decent person.