You may notice the width of the actual text of your email is wider than your images. You may also notice the images themselves are not centered.
If you notice that same email renders correctly as a template but not as a campaign, this could be due to a setting in the footer. To check this, navigate to the Footer section by clicking on Settings, Account Management, Footers, then Edit that specific footers. Un-check "Inherit Styling from Email" and click Save.
You will need to go back into the campaign itself and re-save so the new footer takes effect.