If you observe the syllabus of Computer Science & Engineering- Information Technology, for GATE, then you will be observe that there are 10 broad sections which are mentioned below-

• Engineering Mathematics- In this section, except discrete mathematics all the things are there which are also there in 10+2. But it doesn't necessarily mean that the student need to be as rigorous as JEE ADVANCED MATHEMATICS.You should check the previous year paper, and you will find that the question are much easier compared to that of JEE ADVANCED. So without any doubt, prepare for the syllabus itself, no need to focus on JEE level mathematics.
• Digital Logic
• Computer Organization and Architecture
• Programming and Data Structures
• Algorithms
• Theory of Computation
• Compiler Design
• Operating System
• Databases
• Computer Networks

As you can see there are 10 sections, so don't worry at all, even if 1 question comes from JEE ADVANCED standards, still you have all the other subjects to cover up. So don't worry about this.

To download the syllabus of GATE consider the link below;

https://gate.iitkgp.ac.in/gate_syllabus.html

For more information regarding GATE consider the link below:

https://engineering.careers360.com/exams/gate

I hope this helps. Wish you a great eve!