Layer Y=0: radius 3
Build this as a 7 x 7 Minecraft circle.
A simple 3D circle can be planned as stacked 2D circles. Each Y layer gets its own radius, then you build each grid from bottom to top.
Build this as a 7 x 7 Minecraft circle.
Build this as a 11 x 11 Minecraft circle.
Build this as a 13 x 13 Minecraft circle.
Build this as a 11 x 11 Minecraft circle.
Build this as a 7 x 7 Minecraft circle.