It appears the gasket lines up OK with the bolt holes, and fully covers the outer edge of the flange, so it will be sealed.. I can only imagine, that there is no manufactured gasket suitable to follow the exact shape of the header opening, so they just supplied one that would seal around the edge.
That gasket material in the opening could all be removed, or it will remove itself after awhile. When I pulled my side-pipes, (which use that exact gasket) off for painting, after 5000 miles, there was nothing left in the center at all. It had all been burned away and blown out.

Many builders just use the high temp copper RTV at the flange, instead of gaskets, and with great success.