When I hit the send button it sends the email then comes up with just the header and no thank you message

Hi James,

when using headers in PHP make sure there is NO output before you call the header function.

In your case you have the line:

header("Location:index.php?status=thanks");

But you also include your header file with:

include('inc/header.php');

This file contains output (in this case some html code) causing your header function to fail. From the PHP documentation:

Remember that header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP. It is a very common error to read code with include, or require, functions, or another file access function, and have spaces or empty lines that are output before header() is called. The same problem exists when using a single PHP/HTML file.