Dua is two kinds. One is dua with action and other one is dua with pray.
Allah made this world with rules. Physical rules for every creation(like gravity or composition of water), and moral rules for society(this includes all religions from Adam).
To be successful in exam, you need to know answers of questions. To know answers of questions you need to study first.
Studying your exam is a dua to Allah that you want to pass your exam.
Allah created this world with rules which we have to understand and obey. Just praying and asking Allah to change this rule is like this: You are a child. Your father ask you to do your homework for tonight.If you do your homework you will be rewarded.If you don't you will be punished. He worn you. Somehow you didn't do your homework. And last 2 hours, you are buying your father flowers and perfumes. You are writing best poems to your father. Is it change result?
Yes, Allah can do anything, any time. Yes, somewhat Allah can put all information to your head instantly. However, if Allah do always what people ask, what would world become? Everybody sits and just pray for what ever they wish? (Plot twist: Heaven!)
People who understand physical rules are studied to exam. If Allah do as you ask, where is the justice for those who studied?
What should you do is study your exam (This is also a pray/dua). If time is not enough, do at least your best to study. (studying 2/3 of the night may be enough to pass your exam? In collage, we did that also)
What should you do if you can't pass exam? You must realize this was a example for reality of this world. You have to obey rules of this world which Allah created. This was just a good experience to learn. You may not continue this education but you may find other education opportunities. (Which demands search and study also)
Most of all you need to learn pray with action. If you do any actions of yours(of course which is not prohibited by Allah) to get consent of Allah, your actions will become pray/dua.
