What are your project properties?
What are your render properties?
If your rendered output does not align with what you are seeing in the preview, I’m gonna guess that your render properties do not match your project properties. Especially if they are using different aspect ratios.
The other thing to check is to turn your preview window to Best (Full) and check if things still look the same. This is the setting that will be used when rendering.
~jr
http://www.johnrofrano.com
http://www.vasstsoftware.com