I made a large document in Excel 2016 that I want to "print" on Din A1 paper. I want to send it to the printing provider after first saving it as a pdf.
I have set the sheet to fit on one page in the "Page Setup" (see Screenshot).
I then selected "Manage Custom Sizes..." from the "Paper Size:" menu since I want to print it on A2 or A1. - Set the custom size for Din A2 and Din A1 using the drop-down menu:

Though the result looks like this:

As you can see, the sheet should cover the whole page, but it doesn't with this particular custom size.
Neither does it fit any other custom size, which is above 297mm x 420mm, which is the supported DinA3 size.
When I use a custom size of 297mm x 420mm the sheet fits the page well, but even if the custom size is just 1mm off the results breaks.
See the following example with 297mm x 421mm:

How do I print out this Excel Sheet on ONE custom page with custom size? (Like Din A1 with 594mm x 841mm)