Ranking in .co.in but not in .com

Hi

I am working on an amazon affiliate site and it is currently ranking on first page for few keywords in google.co.in

But its not ranking on first page of google.com, it is currently on second page in .com

I have targeted usa as my target country in webmaster, still i dont know why it is ranking well in .co.in and not in .com

Any suggestion what should i do so google will give preference to .com ranking and not .co.in

Note:I am from India