Hi mixedmedia,
You can hide the sidebar two ways.
1) Add this to your custom.css:
.sidebar { display: none; }
The advantage is this will hide the sidebar from view. The disadvantage this leaves the content aligned left.
2) You can create a dynamic template under Corona > Template Builder and set the Dynamic Page Template Layout to "fullsize, no sidebar" then save. Once you've done that, you'll need to add the other elements as you see fit like "Post/Page Content". When you're done go to the blog post, on the right there's a box called Page Layout. Select "Dynamic Template" then whatever you called the template you created.
Hope this helps!
Regards,
Mya