The default configuration for the Squarespace RSS feed that is being generated

If you want full text to appear in feeds, there is a configuration option available and you would simply need to login to your website, access the configuration menu for your journal page:

http://help.squarespace.com/customer/portal/articles/10770-reconfig...

then scroll down to the XML/iTunes Syndication section and adjust the XML Feed Presentation settings so that the page is configured to include full text in feeds by default.