What renderer are you using? Tex filter or MathJax?
MathJax has two output formats - inlineMath and displayMath. Everything inside displayMath-delimiters goes to a new line and everything inside inlineMath-delimiters goes inline (to the same line). So if you are using MathJax check the delimiters...
If you are using tex filter each tex image has a class "texrender" and from core themes only standard theme and splash theme have the necessary css for displaying mathematical notations inline centered. If your theme does not have this css, you can add it to one of your custom theme css files