I am assuming that you are using standard header formatting with a center and right tab setting. With your non-printing characters displayed, you should see a tab character (small arrow) before your centered text. Put the page number before that tab character.

If I am mistaken, change the alignment of your header text to left-aligned. Then place the page number before the text and press the tab key to center your text. (For the one on the right, left-align the text and press the tab key before it. Then go to the end of the text, press the tab key, and insert your page number.)

For your leisure reading:

• Basic Concepts of Microsoft Word - by Shauna Kelly
• Alignment / Justification of Text in Microsoft Word
• Basic Formatting in Microsoft Word
• Sections / Headers and Footers in Microsoft Word 97-2003
• Understanding Styles in Microsoft Word

In a relatively short time, you will save time by reading these. Word is a fairly complex program that Microsoft likes to make look easy. It is easy so long as you do not try to do much more than a letter. With lengthy documents and multiple headers/footers, it can feel like the program is trying to work against you if you do not have an understanding of at least some of its complexity. I realize that you are using the Mac version and these are Windows articles, the concepts are valid in the Mac version, though. You may have to find equivalent commands.