You do not Export the chart. You must Print it to a PDF printer like CutePDF (free download). Get your chart laid out in FTM so you have the measurements; make sure there are no page divisions so it will print on one page.
After you have the chart set up, close FTM, Before opening FTM to print the chart, make the PDF printer your default printer in your computer's Devices and Printers. Set the paper size in the printer properties to a Postscript paper size big enough for your chart. Then, open FTM, create your chart, select Print and send your chart to that printer. If all goes well you will end up with a pdf file to take to the commercial printer. Make sure in the PDF preview that there are no page divisions.
This problem is not unique to FTM, It is a problem for most chart software, and is caused by a change in MS Windows a few years ago in the way printers and paper size are handled.
Good luck - it may take a few tries to get it right.