This is very hard for someone in the US to answer.  Maybe someone with DOEACC experience here or in India can help?
 
I looked over the O and A-level DOEACC curriculum and my impression is the 'A' is not a good stopping point.  It skimps on operating systems by focusing on applications but has a decent treatment of graphics.  Nice to see the references; I personally know at least two of the authors listed there! (Woo & van Dam)
 
If you're asking what to study, where to specialize, the answer depends COMPLETELY on what you intend to do with the education.  If you want to become a software engineer and build cool things that can change the world, focus on software methodologies & OO, operating systems, database systems, and web development.  Otherwise pick a speciality (like graphics) and learn everything there is to know about it.
 
If you goal is to get a good job in the field, here's a tip.  I have hired many, many programmers over the years (in Silicon Valley, USA) and, like a lot of my colleagues, I look for what someone has done OUTSIDE of classroom work more than what they did inside.  Your hobby projects speak more about your drive ans skill and do your grades, in my opinion.