You don’t have a machine selected. If you have the SM config file for Fusion installed you should be able to select your machine.
I’d turn off the “round up to nearest”. Fusion is designed for pro use and most cnc businesses use preset stock sizes so that’s why that’s there.
Is your stock size your actual stock size that you entered? Or is that the size of your model?
Have you read this thread:
https://forum.snapmaker.com/t/some-info-on-cnc-tool-changes-and-combo-cnc-laser-projects
-S