If you already have issued your character certificate then it is absolutely fine to make it in BTech. You don't need to get a new one.
Candidates can check B.Tech Cut off for Top IITs & NITs here.
No you need not make another character certificate. rest assured you need not worry about making any other certificate only because you are a dropper. As you have a certifocate already issued from school, you dont have to get it reissued
All the best.
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