I’m not sure I get your problem correctly.
I think it has to do with the white edge that is still here?
If that’s the case it is normal. With the pixels, you can’t draw a perfect circle. If you had just full black and full white color available, you would be able to draw something that look like a circle but that is really harsh on the side if you look closely.
To avoid that effect, the computer is cheating and he is adding some pixels on the edge that are not fully opaque. Those pixels are there to smooth the edges.
It is called anti-alliasing and here an example:
That’s what is happening in your case. Since some of the edge pixels have some transparency, you can still see a bit of the white beneath it.