This plugin does not show the full content of each feed item. You can optionally configure it to show the feed item description, which is something slightly different. This may or not be what you want.
If you are editing the plugin, keep in mind that your changes will be overwritten if you update the plugin when an upgrade notice appears for it. Better to request this as a feature instead.
Regarding that RSS feed, I was able to display it on my site using the latest version of the plugin (1.4.2). So I’ll need more information to diagnose the issue.
However, if you have manually edited the plugin, you’ll need to reinstall the stock version of it before I can debug. I can’t help you if you edit the plugin and break it.
Of course, if you have not manually edited the plugin, then please post a link to a page where you have included the shortcode so I can see what is happening.