Hi, joanajoana. Your problem lies in the nature of paragraph styles. By definition, a paragraph style is applied to an entire paragraph. Thus, Word is picking up more than you thought you had included in your style.

Although I haven;t tried it out in this case, I believe that what you need is a little-known Word tool called the Style Separator. you can add it to your Quick Access Toolbar by going into your Options, selecting Customize, then All commands from the drop-down at upper left, and scrolling down to the Style Separator. Select it and click on Add.

If you have your hidden characters showing, which I recommend, it will appear as a symbol comprising two paragraph marks. You'll need one before the heading text and another after it. This will allow you to style the previous and following text in your text paragraph style, and your heading in your heading style.

Hope this helps.

Best,
Ulodesk