I agree with all the suggestions above. Just wanted to add that the bitmap editing in GIMP (jpg, gif) is fine, but the vector Trace in Inkscape is what lets you scale the size without creating those messy jaggies. You probably know that you can save the jpg, gif, bmp, etc. from GIMP, load it into Inkscape, create the vector trace, save as SVG from Inkscape, load the svg into GIMP, and go back and forth as needed.
When resizing, it's best to do in Inkscape to keep the smooth edges.
But note that you don't follow the jaggies with the scroll saw blade - it acts like a filter to remove that high frequency noise when you make the cutting.
BTW - nice one, Mahendra.