I need some help

[egyptianblue]

So I've been working on the Cathedral Rose Window pattern since October and I have finally gotten stuck. I have finished the large heptagons and the black round that follows but I don't quite understand how to make the half circles. Can anyone please explain it to me? Or any advice to spare? Thanks.

[mathwizard25]

Are you doing the afghan? Is it a doily?  A little more information might be helpful.