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Actually what you have done is perfect - and turned down edge is not the real issue here.
If the aperture stop is not a smooth circle, you will get a lot of scattering as is evident in the lefthand image; making the aperture stop a smooth perfect circle results in a lot less scattering as shown in the right image - and you have hidden the three mirror clips as well.
The typical Newtonian mirror has a bevelled edge ground with a coarse grit, which means that without anything else, the edge of the mirror acts as the aperture stop - being rough, it scatters a lot of light and degrades the contrast on planets too, BTW.
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