I built 30 some odd years ago an old B-2 model from the Israel Air Force magazine. It was in 1:50 scale and had no internal details. Not the same as your version from Model-Kom. So that does not count.
Anyhow, since this is a flying wing design with an internal bomb bay and landing gear bays, you need to insert either a wood dowel, carbon, or metal rod thru the wings and fuselage to prevent a sag.
You may want to consider inserting the dowel one in front and one in back of the bomb bay that extends thru as much as possible.
Also, you can add the dowel/rods along the leading edge and into the fuselage. Either Super glue of epoxy the center.
here is schematic for your consideration
Isaac