As jj77 says, there are two ways to build an FEA model of a honeycomb core sandwich composite panel.

I used a solid block and assigned orthotropic properties to represent the behavior of the core without having actual hexagonal cells.  This is an efficient way to model the panel.

The other method is to model the actual honecomb cells made of isotropic aluminum foil in hexagonal (not octagonal) shape.

Note that the wall is double thickness on 2 sides and single thickness on 4 sides.

Please reply and clarify which approach you are taking.