I sounds like you have borderless set in the driver, that expands the printable area size.
Check your driver settings from within Q.
Terry

Qimage can't show the wrong paper size: it is showing exactly what the driver reports and the driver is reporting 303.9 x 215 mm.  So the answer to "why" lies somewhere in the driver.  One place to look is in the page setup tab of the driver.  If your driver has an "Output Paper" selection, make sure that is set to "Same as paper size", else the driver expands the paper size internally.

Mike

With many Epson drivers, when you choose "retain size", instead of "auto expand", the driver actually expands the paper size slightly beyond the edge of the paper.  In this case, it looks like Epson "falsely" reports the paper size as larger than the physical sheet by about 3.5mm on the left and right edges and about 2.5mm on the top and bottom edges.  They do this because with "retain size", if you specify an A4 print on A4 paper, you get exactly an A4 print but if they report the physical paper size as A4, you would never have the option to bleed beyond the edges manually if you wanted to (to avoid slivers of white due to imprecise paper loading).  To understand why they do this, consider the way borderless works.

Many drivers don't even offer the "retain size" option that you've chosen in your screen shot and they only offer the "auto expand" option.  With "auto expand", the PPI of the driver is listed incorrectly at something higher than the actual: like 730 instead of 720.  This forces software to see the higher PPI (730) and it, in turn, will send everything at a slightly larger size than requested due to the inflated PPI value.  Even if you print on a borderless A4 sheet and only print a 5x7 in the center of that sheet, your 5x7 will actually be expanded by a multiple of 730/720 making your 5x7 actually 5.07 x 7.1 inches in size even though you didn't even need borderless to do that print.  This is how auto expand works: so that if you print an A4, it'll be expanded slightly beyond the edges of the paper so you get full bleed even if the paper loads a fraction of a millimeter off.

Moving on to "retain size"... With "retain size", you actually want the paper to be reported slightly larger than physical!  Why?  For maximum flexibility.  If you print a 5x7 in the middle of an A4 sheet with "retain size", your 5x7 size is still retained: it's still 5x7.  Good so far: smaller size prints are not artificially inflated in size.  But if the driver didn't give you some "bleed slack" at the edges and it reported the paper size as 297x210, the biggest print you could send is 297x210 and because no paper loader is perfect to the micron, all your A4 prints will likely have a little sliver of white on at least one edge.  To allow maximum flexibility, they actually let you print to the left of the left edge, to the right of the right edge, to the top of the top edge, and to the bottom of the bottom edge just a bit.  This allows you to print a 303.9 x 215mm print and get some bleed beyond the edge of the paper using that size if you like: ensuring full coverage of the paper.

What does this mean for Qimage?  If you want to print a single A4 on an A4 page, it's simple: choose A4 size and use center positioning.  For multiple prints within an A4 "space", I'd recommend going into the margin settings (from Qimage's top menu) and adjusting the "additional" margins so you get a 297 x 210 printable area (to counter the fact that the driver is giving you printable area beyond the edges of the physical paper).  From your screen shots, it looks like you'd probably have to enter a 3.5mm additional margin on the left and right and a 2.5mm additional margin on the top and bottom.  Once you set that up, you've basically countered the driver's "beyond the edges" sizing and you can save that printer setup for future use.

Keep in mind that if you position a print at 0,0 (top left), you are actually positioning that print partly off the page due to the above: because the printable area actually extends slightly beyond the edges of the paper.  That's why setting up the margins to counter that is the answer.  Just be aware that doing that is a tradeoff in that if you try to position (one or more) prints in an A4 area on an A4 sheet of paper, paper loading comes into play.  If your two prints add up to exactly 297mm for example, you can expect one of those prints to have a small sliver of white at the paper's edge while the other one will have the same size sliver missing on the other edge simply because there is no way to load paper perfectly and you are at the mercy of the paper loading mechanism.  If you print 297mm worth of print area on a 297mm piece of paper, you are asking the paper loading mechanism to be perfect and it simply cannot be.

Mike