Just scaling the paper from A4 to A3 doesn't help much if no more data is added to the print out by picoscope 6. Compare that to the situation when you zoom in on the screen to see a waveform better, picoscope adds more and more data from the waveform memory to display the spot you want to look at with best possible resolution. If you just zoom without adding data the waveforms will be more and more "pixelated"
The same should be done when moving from A4 to A3, more data should be added from the waveform memory to display the best possible waveform.
The suggested solution to scale in the printer driver will not add any data to the waveform which means that it is quite useless.