I am totally new to inkscape...so sorry if this question has a very obvious answer....
I have been following this tutorial:
https://www.youtube.com/watch?v=w3Wr_XfMFbU
but when I select 'Interpolate Sub Paths' from the Path effects editor the circles over lap to create negative shapes:

How do I get it so that the shapes just overlap and don't create the negative areas?
When I then click 'perform path' I get this:

...one of the circles is not filled.....
I am not sure achieve the same result as the video - where all the circles are filled.
Many thanks for your patience (if you read this far).
J