Hello, my first-choice university for my bachelors is Duke University. Please suggest me how to go about it and give tip

Your SAT is excellent for a Duke applicant. Your GPA seems sort of low, but considering that you're in the Indian system that may be a consequence of whatever conversion factor you were using. I don't really have enough experience with the Indian system to be able to tell you how good of an applicant you are academically anyways. Admissions officers, however, will be able to interpret your grades accurately, I'd assume.

The fact that you need a full-ride scholarship will be held against you. Duke is not need-blind for international students. Unfortunately, I think that significantly decreases the competitiveness of your application.

I think your portfolio of co-curriculars is the real issue though. Considering your interests, maths and compsci, your portfolio doesn't support that whatsoever. Trust me, your co-curriculars are far more important in getting into a good US uni than your grades (unless they are really bad).

Your interest in football only really matters if you're a recruitable athlete, which, by the sound of it you don't seem to be. It could be a pretty sweet personal statement, though, and it's certainly something worth listing on your Common App, but it's more of the thing that fleshes out your portfolio a bit more than the centrepiece to a good set of co-curriculars. The same thing can be said about the social entrepreneurship program. In general, you should have something that shows your own initiative. An experience where you're not working under the mentorship of an established program, but where you're doing stuff yourself. That's really what's missing; this sort of initiative-based centrepiece. And even a really prestigious programme, like the RSI or the SSP, can't replace that.

I don't think it is possible to set up something meaningful along those lines in 2-3 months, though. You'd need about half a year of the project actually running (so not including any time you just spent planning the thing out and negotiating with stakeholders), at least.