Passing the written exam and getting shortlisted for the interview is a great achievement! While the interview is an important step in the JNCASR admissions process, it's not the sole determining factor for your admission.

• Evaluation: The interview is a chance for the JNCASR faculty to assess your:
  
  
  • Scientific knowledge: They'll delve deeper into your understanding of concepts covered in the written exam and related areas.
  • Problem-solving skills: They might present you with a problem or scenario to gauge your approach and analytical skills.
  • Research interest and motivation: They'll want to understand your passion for research and your suitability for a specific research group.
  • Communication skills: The ability to clearly express your ideas and thought process is crucial.
    
    
    
  • So, even if you don't feel you perfectly nailed the interview:
    
    • Don't despair: There's still a chance of getting admitted. Your overall application strength plays a role.
    • Focus on what you can control: While you can't change the interview, focus on showcasing your strengths in the remaining aspects of your application.

https://www.careers360.com/university/jawaharlal-nehru-centre-for-advanced-scientific-research-bangalore

I hope it helps!