Official comment
Hi Scott ... in WordPress, the theme's stylesheet will often cause the form to be left-justified. In the page editor, click the "Text" option to reveal the form code and add the line above and below shown in yellow:

Some themes will still overwrite the in-line CSS we have provided above. You can try a few other options, such as the following (these are in order of success after the first method above):

Or -

As a last resort, you can increase the left margin which almost all themes will allow:

If none of these work, contact the theme author for instructions.