I think you’re just looking at the model. Fusion won’t cut your actual design model. You have it cutting to the bottom of your design, but that cut is not modeled. Turn off the visibility of the model, so you only see the simulated stock.
Typically, just make your design look like the end result…I think you’ve been overcomplicating things in Fusion quite a bit. If you want to cut a rectangle, design a rectangle and then set your toolpaths to cut that rectangle. Why are you designing this and then cutting a rectangle?
