Parent margin changes don't affect document text boxes

Hi! Sorry if this has been asked before, but I couldn't find it. I'm going pretty crazy and up against a deadline. 

My parent spread margin doesn't affect the text boxes that make up the entire document. It's a full-length paperback book. I've included an image....   Pink line is where the parent spread has asked the bottom margin to stop at, but the blue line is where the document (text box) has decided to stop instead. How do I change it? I've been searching for hours!