Heyy Raj....

This is the eligibility criteria for B.Sc students appearing for gate this year: 

• Passed a Bachelor's degree in Science (Post-Diploma/ 4-years after 10+2) or currently appearing (4th year) of degree
• Year of qualification must not be later than 2019

And for CAT , you just need to have your graduation done.

You can give in you're more interested in pursuing your career in management fields such as HR , finance , marketing etc and giving GATE will give you opportunity to pursue masters in your respective technical field that you did your graduation from.