Like any other competitive examination in the country which includes mathematics, ALL the topics are important.
In the Previous Year Papers of CIC B.Tech. Entrance Exam, you’ll find that the questions are generally inclined towards Calculus; so getting an exceptional grip over it should give you an advantage.
But as I said, EVERY topic is important.
In 2017, there was a nice easy paragraph question, which included 5 questions, i.e. 20 marks.
An entrance in which a mark is differentiating between the ranks, you know you cannot leave even a single topic untouched.
All the best.