How can I get 90+ in boards

In 12th so far the most I’ve studied for an exam is 2 hours. My highest marks out of 80 are Legal studies 72/80 Accountancy 22/80 BST 29.5/80 Eco 32/80 I really need help as without 90 my chances of uni are gone, im willing to put in my 100% now so help would be appreciated.