You are getting the double-image because the Postscript PICT option is selected when you are exporting the graph as a PICT. When going to a drawing application such as Canvas, try using the High Resolution option. You can also export as a high resolution TIFF file.
KaleidaGraph is a thoughtfully designed graphing and data analysis application for research scientists, as well as for those in business and engineering fields. It produces publication-quality graphs, and easily converts the most complex data into a functional display.