Paint.NET :: Save Onscreen Image (Near 100%) As Final Image Size

If I load a large image (say 5400 px sq.) in Paint.net (or similar) & choose a zoom level where I like the look / size of individual elements, in ONE area. Image is still no where near 100%.
 
I select a rectangle so the ACTUAL size of rectangle_AND the way the selection looks AT THAT ZOOM level, is what I want. Say, to use as Fx header background.

Problem I've had: Because the image I initially cropped wasn't at 100%, when crop it - the PHYSICAL size of the rectangle may be 1920 x 180 px, but the prgm still thinks / knows it's really 3500 x 450 (or such), at 40% zoom. I can't just save the image - as it looks on screen - & it be that size when reopen it.
 
I DON'T want to resize / resample it, because (sometimes)  that changes the current look (size of certain elements in the image). The only way I've found (gotta be another way) is take a screen shot of the cropped image, at it's CURRENT zoom level. Then it will save as a 1920 x 180 px image, NOT as a 3500 x 450 px image that was at reduced zoom.
 
If I resize & save at a REDUCED %, it can change the look & size of elements. Every thing I've tried to save the image - at it's PHYSICAL size on screen - say 18.5 in. x 1.75 in. (when image is NOT @ 100% zoom), results in saving a much larger image.  I understand this, but looking for a way around it.  Used various settings & tried to trick the apps many ways - cropping in one app, copying to another - you name it.