Saving as a pixel size in In Design


I am trying to make a poster 800x600 pixels in InDesign. When I open a new document I set the increments to pixels and then set the page size of the new document to 800 x 600 pixels. I then design the poster on the 800x600 document. Once completed I go to file, export, change the format to Jpeg and then save the file. I've then gone to upload the image to an email as well as a restaurant POS display screen and the image is showing up as 2333 × 1750 pixels. Can someone please tell me why the file saves in such a bigger pixel size - when I have set up the document as 800x600 pixels? And how do I resolve this problem?

Thanks very much for your help!

10/20/2014 9:45:00 AM