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.
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.