I tried your script and adjusting the offset of the ylabel seems to do exactly what it is supposed to do. The plot even resizes (unsquashes) itself. I'm using gnuplot 4.4.3 on linux. Perhaps your version behaves differently?
Lee Phillips
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gnuplot Cookbook...
Your data might already be in grid form, depending on how it is organized. Type "help grid_data" at the gnuplot interactive prompt to find out what this means. Even if it is not, the plot might work. Try it and see. If your data is scattered you might be able to plot it after letting gnuplot...
Assuming your file contains grid data, the basic commands to generate a contour plot would be
set contour base
unset sur
set view map
splot 'file'
gnuplot will generate a key mapping dash patterns in the contours to values. If you want actual numerical labels printed on the contours...