The single review email template doesn't have an option to restrict the header and footer to a certain width, I'm afraid. But I suggest using the custom email template. In the custom email template the header and footer width will be the same as the rest of the email:
Let me know if you need further assistance.
The heading and footer of my emails are very wide. Is there anyway to reduce width to a more normal size, like 600px? In image, you'll notice that the colored bar extends far beyond the text.