I am lucky, that I only need titleblock dimensions exact and not the drawing dimensions.
Screenshot from my schoolbook.
600x400

Thank you for quick reply!
My country has a dumb regulation for titleblock - has to have perfect dimensions - this was the reason, I started this mess with pixels, milimeters and scales. When I become electrotechnican in 4 months, I will not have to observe perfect titleblock dimensions anymore (...), but now I am in school and if it is not perfect, I am in trouble. I even saw Russian collegues have made their own titleblock as element.

As soon as I posted this question, I had another careful look in the pixel columns - I took wrong width value of 2245! Should have used 1587px. Much harder to make perfect columns x pixels calculation now, but I got a perfect match!

Hi everyone!
First of all - big thanks to developers of this superb software!
It is way more easy to learn than Autocad, which will not be very useful for electrical schematics.
I have one small problem though. I am sure that it is because I do not seem to understand about mm to pixels or something.
I am planning to draw some schematics on A3 paper. For that I need folio of 1122 x 2245 px (297x420mm) 
I created a folio with 22 columns of 102px and 11 rows of 102px (cannot get perfect match, but very close.
I started drawing and in the middle, had idea to do a test print, and... my folio has wrong proportions. 
600x400

Is there anyone that can tell me what I have misunderstood?