It sounds like you are bringing it into estlcam as a STL. That will bring you into 3d machining and take a LOT longer. You need to bring a DXF into estlcam and then set up your cuts.
This post will help you get a DXF from fusion… Design vs. cut differences - #32 by Jonathjon
And this will help with setting up your machining… Milling Basics