It looks like Phillip was able to help you with the issue you were experiencing, which is great!
For everyone else's benefit, formatting issues can occur for various reasons. If the mailing is being viewed on mobile, it will look slightly different than the desktop version. Also, different email clients render emails differently; it can appear differently in some clients. And finally, there could be an issue with the content that is causing a formatting issue upon send. This can often happen if text is copied and pasted from another source or the html has been manipulated in some fashion; the coding behind the email is altered and will render strangely upon send.
Hope this helps! Let us know if you have any other questions.