ThorHammer

Logicsound! I am also strugglig with PHP, but just relax, there is millions of extremely skilled people out there where you can get help. I am not sure if I am violating the rules by naming a site I am using when I need help, if so, any moderator must forgive me and delete my entry, but, when I am seriously stuck, I am using freelancer.com.
Try them, logicsound, you will be amazed.

Your newsletter and your post template got different css values, I presume.
If you want your blog to have the same css as the newsletter, you must modify your style.css.
Or, if you want posts containing the newsletter to be styled in a different way than the rest of your posts/your site, you can make a separate CSS and attatch it to posts posted as newsletter via conditional tags. This can be done by assigning your second stylesheet via categories, for instance. So, in your functions.php, you will have to add
the tag is_category('id for your newsletter category')
Read about conditional tags:
http://codex.wordpress.org/Conditional_Tags

Just have a look in the default theme shipping with wordpress. The solution lies in sidebar.php and style.css.

Copy index.php and name it page.php

Then, create css for your page.php and define all content to exist within one column.
Like, for instance:
#page_template_wrap {width:100%;text-align:left;}
and then create styles beneath this wrap, like:
#page_template_wrap .content {define your content styles inside the page wrapper}
Be sure to keep everything within the page wrapper in order to have only one column.

Then, in the end of page.php, remove the
<php include_sidebar(); ?> (If it is there).