how much percentile i should target GEM candidate

Your excellent 10th and 12th scores help, but as a GEM, the 6.8 CGPA makes admissions more competitive.
Target 99.7–99.9+ CAT percentile for the best chances at BLACKI and FMS, while 99.5%+ keeps you competitive for several other top B-schools.

Target 99+

But here's a random thought ? Let's say I ( taking my example), think of scoring more than 99%ile and I know that's my target to get into the school I have in mind, will I get it ?

Just by knowing what marks to get ? Will I actually get them ??

My personal advice to you will be, always aim higher, and study! Please do not think how many marks to get, what chances I have, what schools are available?

We're in July, first we study and then we think later.

All the best ☺️💯
I hope it helped!