I would suggest: In Paint, click on File, Page setup, Paper size:A4. Orientatation:Portrait. Scaling:Fit to 1 by 1 page.
In the Page setup window you will see at the left a 'preview' of your settings. The grey rectangle with a cross in it (that makes it look at first like part of an envelope) is the actual picture and shows size and where on a sheet of A4 it will print. so if only part of the 'grey envelope shape is showing then it will only be printing part of the picture on each sheet of A4, so you need to adjust the scaling to fit to 1 by 1 page.