Extra line after Swept Cut + Swept Boss

Hi,

I am working on adding a wall to a structure that was previously empty (First image). Since I need it to be at an angle, I performed a Swept Cut (Second image) with the desired inclination and then used a Swept Boss (Third image) to create the wall. However, after adding the wall, a line appears (Fourth image) as if there is a slope, but I don’t see any actual slope. How can I make this line disappear?

First image: the previous empty structure.
Second image: Swept Cut
Third image: Swept Boss
Fourth image: the line.

Any help will be really appreciated!