Don't feel bad, you're not alone there... I've been doing dumb things working on cars lately. Best to keep away from CNC machines until my brain comes back from vacation...
BTW - One more small Fusion tip - I noticed you seem to have added a special plane just to use for mirroring the first body. You don't need to add that plane - just use the face of the first body as the mirror plane.
Regards,
Ray L.