How do I change the margins in a particular section for a Word template?

Hi all,

I'm trying to set up a Microsoft Word template where the top part is automatically indented, and the rest of the text isn't. 

So far I've inserted two section breaks, and changed the margins accordingly, but the issue is that section breaks aren't fixed, so the breaks move around. (Please see the screenshot below.) How do I fix the section breaks, or is there another way to go about this?

Thanks in advance for your help!