Sorry no way of trying out in Galaxy Watch Designer/Studio - whatever that is. The image you posted - image3.png - is from your Mac ?
It is 16 bit precision, you could try again with 8 bitImage -> Precision then set 8 bit
The only other possibility is if somehow the Mac Gimp imposes a different x / y pixel resolution. You can check by toggling View -> Dot-forDot on off.
This the same image 360 x360 pix with the y resolution half the x resolution. Gimp is a pixel editor dot-for-dot is normally on. Dot-for-dot-off gives a real-world view.
Otherwise - do not know, some strange MacOS thing.
It is 16 bit precision, you could try again with 8 bitImage -> Precision then set 8 bit
The only other possibility is if somehow the Mac Gimp imposes a different x / y pixel resolution. You can check by toggling View -> Dot-forDot on off.
This the same image 360 x360 pix with the y resolution half the x resolution. Gimp is a pixel editor dot-for-dot is normally on. Dot-for-dot-off gives a real-world view.
Otherwise - do not know, some strange MacOS thing.