can't find any settings to fit the image to the page.
There is a Custom setting for Fit to Page that is a;lso near the bottom of the size drop-down list, see attached screen shot.
The reason I need to rotate the images is that there are often a mixture of portrait and landscape shots that are to be printed on a contact sheet.
Do you mean you want portrait shots to be on their side?
If you have a square template for a contact sheet all the contacts on the page will be the same size. See attached sample.
However, if you want every one to be "landscape" so portrait shots are on their side then I think you will need to turn off auto rotation in your camera or, as you say, edit the exif data.
To do the latter the best software is ExifToolGUI. It uses ExifTool, a Command line program but provides a GUI fore easy use, and it's free.
See
http://freeweb.siol.net/hrastni3/foto/exif/exiftoolgui.htmThe link in there to download ExifToolGUI and ExifTool (which you need) with all the instructions.
See screen snap for part of GUI, not very clear but give the program a go, it's very useful.
Terry