Resize Text: long text does not stretch in Autolayout

Hi I’m Aya, beginner.
I tried to make an example from Figma education.
I can not resize text box.
The yellow one is what I want. The text stretch when you make the box wider.
But mine (red one) 's text stay the same. when I make it narrower , it works fine.
The setting looks the same as example.
What am I missing?

Thanks in advance for your help!

Its width is already set to Fill, but there are line breaks in the text, forcing what seems to be a fixed width, but isn’t. Remove the line breaks so the text flows.

Thank you so much! I could fix it:)