I had a problem very similar to this, even though I did everything else right. See if my solution works:
Go to 'image properties' under the image menu. see what the resolution is. The resolution I needed was 72.009 x 72.009 ppi.
Go to 'Scale image' under the same menu. Instead of scaling the size, scale the 'x resolution' and 'y resolution'. You can try 72.009 and see if that works. If not, you can expiriment until it does.
I hope that helps!