3D Cubic fractal

This is a 3D fractal made for a math project with the 123D Design Software. The base is a cube from which each face is divided in order to obtain a tiling pattern of 5 diamonds with the same area. On each face, the middle diamond is kept and the 4 others around the middle one are extruded in the 3D modeling software. The pattern is repeated in the middle diamond. For this project, the pattern was repeated 3 times. However, I encountered a problem which i was not able to fix. If you look at the b