Oh okay, I understand now. You mean taking the exam.
I was under the impression that internationals use IB, an equivalent of AP, but there’s nothing wrong with taking AP either! This link (http://apcentral.collegeboard.com/apc/html/ap-in-india/ap-in-india.html) might be able to help you out a little. I think self-studying it and taking the exam shows that you are pursuing rigor and will definitely give you an advantage.
You should do both: work hard on the SAT, school, and the AP tests. It depends on how much you need to improve your scores, but I think you’ll be okay with balancing both.