You have Guide Borders turned on which is why those lines are drawn, to aid with trimming. That seems to be what you want, from your description, so I'm not sure I understand the problem. Are you saying when you print it again you see something different?
I see that the small macOS preview window may not be rendering those very thin lines accurately. But that should only be used as a general guide for layout. You should use the Qimage One Soft Proof/Preview function to see an accurate preview of the print.