And the ruler above the heading shows the position it tabs to. From your description it seems that's out of the box. Just move the tab to where you want it, for example inside the box.
I suppose tabs are in the first half of a 1000-page book on Word?
I've had no problem with the header in the even pages of my 20-chapter book. This is the title of my book with the page number at the left (outside). All these are "linked to previous" - the default setting.
But getting the header in the odd pages is giving me problems. I want the chapter title in this heading. I first click the Link to Previous button to get rid of that setting, then I enter the text I want. The problem is this: The page number is outside of the header box - outside of the margin setting, almost to the edge of the page. There is also a small right-pointing arrow between my chapter title and the number. In the even pages the header is clean with the page number on the outside but within the header box. The number on the odd pages is outside too - but why does it appear outside the header box?
I have "Microsoft Office Word 2003: Inside Out" open before me but I see no help in this 1000-page book. Maybe I'll have to get a 2000-page book.