Trying to add datum to corridor and it shows up weird in sections

[FabriCADed]

First image is of my cross section with the topo surface, and proposed assembly (pipe networks are also in the section sources, but no pipes in this section.) The second section is only different in that the proposed corridor surface is shown (created within the corridor properties under the surfaces tab - the surface has the datum code added to the surface as seen in the second image.) My question is what I'm doing wrong to get the datum to show up like that? I'm trying to compute materials and my dirt quantity gets thrown way off by this. Does anyone else see this happen? I'm a noob to intermediate Civil 3d user, but this seems to happen to all the guys in my office..

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[yawlaynpt434031]

The second image may be missing surface boundary. I think you should check the corridor surface boundary whether assign or not.