Following up on what Paul told you...

I agree about using any Heading Style in a header - don't do it. If you need to, you can create a new paragraph style that has the same formatting but without the outline level.

Use a StyleRef field to repeat the text from a heading of a given style in a Header.

The header style, by default, has two tab stops:
A center tab in the center of your page and a right tab stop at the right margin. If you've changed page margins you may need to modify the Header style.

If what you want is the text at the left margin and the page number at the right margin you can delete the center tab stop from the Header style definition and follow your StyleRef field with a tab and then the page number. You can insert a page number field at the cursor location by pressing Alt-Shift-P.