I have a Mac so I copied the pic, went to Text Edit on my computer, selected Tools then Resize. I reduced the height then downloaded it to your story. That was the only way I could do it with the Unsplash photo.

Here is another way to do it with just about every other graphic you can find.

https://medium.com/everything-shortform/medium-pic-tech-editing-your-story-graphic-sizes-can-be-a-puzzle-if-you-dont-know-these-quick-ed2b601813c5