I think you are over-reacting to what someone who probably knows a lot less than they claim says.
It is completely implausible that any manufacturer could produce a clone of a top of the range phone (in fact, the most powerful phone on release at the moment) within a month of its being available.
Samsung is one of the world's largest companies and will have spent a fortune developing this phone. It simply is not possible that another, much smaller company could have copied it in the time they have had. In fact, I don't believe it would be possible ever.
If your phone does what you would expect, and looks well made, there is absolutely no way it could be a fake. This is a fuss about nothing. I have also searched for "Samsung Galaxy S II" fake on Google and there were no references that I could see on the net to fakes.
However, if you are daft enough to believe this, contact Samsung and ask them.