[Cube with inner structure: not enough outer walls]

Hello

I creatd a test cube with some inner elements.

If I print it I can see the inner structure at the outside of the cube.

In Cura I noticed that the reason is maybe that he only print one outer wall. The inner wall are seperated to print the inner structure.

I think a picture tells more than my bad explanation: lock at the corner with the inner parts.

Is there a way to change this?

 

(by the way: I'm new in 3D printing. Therfore sorry if this is a stupid question)