OK, now I understand all of the issues, but it will be tomorrow till I can create a video on the solution,
1. STEP (*.stp) was always a distractor in this discussion. STEP not needed.
2. ACIS (*.sat) was always a distractor in this discussion. STEP not needed.
3. Inventor not needed - this can be fixed in AutoCAD.
4. Facetres only effects curve conversions to planes - you have no curves to convert.
5. The original document units are shown as foot (-dwgunits), you cannot print a 240ft tile, so scale is needed (either explicitly or by substituting other units, for example 240mm instead of 240ft.
6. And this is the important issue - your geometry is a longggggggggggggggggggg way from the origin.
Move it to the origin and Align with XY coordinates and your wavy side issue will no longer be an issue. (Didn't you notice that I did not have this issue with my original attachment days ago?)
(See Attached file. )
-----------------------------------------------------------------------------------------
Autodesk Inventor 2019 Certified Professional
Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional