Can anybody help me to identify what is wrong with my solution? Getting WA on task 3 and 12 
well this may be problem with precision, i was getting them too when i was using angle sum method to find point in polygon.
because value is going to be as large as 1e9, and we need excellent precision to point out very edgy points, like take example of points (0,1e6) and (2,1e6), one point is above and another is below the line (1,1) -> (1,1e9). check if you code is able to detecte this?
That is not the problem. See AC solution here CodeChef: Practical coding for everyone. Note the commented lines.