DG There are 2 Methods
The Method above gave these results
I tried that out and got a good result Stretching it Equally ans Going Full screen
Zoom the Images good so you cam fill the gaps in
However I think you'll have to figure out a way of reducing the finished article Back to the original size then SAVE It
I tried it at the Larger size of 300 X 300
and Got an
"Out of Memory" error Had to do a "Double reset" switch the Programs off with Task Manager then reset
Suggest you Try a Test at 125% by 125% to start
then Save (If that works increase the Numbers to 150%) Though the risk of it Not saving or working is Determining By how much memory your computer can handle.(Hard drive space & RAM)
I think the clue to its Limits will be to monitor the Resouces in Task Manager It will Turn Red Until it reaches the Top then Freeze the computer,
The 2nd way Which I'd use:
The other ZOOM which is safer is to click View> ZOOM> Custom then You can Max out in anything up to 600%

All you do is reduce to 100% after editing then save