Too much! Too much!
That's not AA, that's blurring. You've added too many pixels to the outside of the object -- anti-aliasing should almost never be thicker than a pixel wide. Also, you don't want to shade *each* pixel, only important ones, where there is much change -- for example, you don't need to AA a 45 degree angle.
Here's a tutorial I wrote a looong time ago.. hope it'll help you.
http://www.rpi.edu/~laporj2/old/essays/aa/