What is considered stretched?

My theme was rejected and all it says is low-quality, stretched, or blank. I was wondering what would be considered stretched? I found a pic on bing that I wanted to use mainly for a theme for myself and decided to mirror it (Have it normal on one side, paste it again next to the original and flipped it so it mirrors). I resized it to be 3000X200 but I do not know why it was rejected. Also is it required to have a footer? I did not notice it until I already submitted the theme but I left out a footer. Might that also be why it was rejected? Would just like answers because I am new to this and really would like to learn about it!

This is the image

Hi Kaitlyn,
the distortion of this image is very evident … the hearts have completely lost their shape and the bokeh circles are ellipses too crushed …
The problem is that many authors do not know that it’s possible to make a preview of their work before submitting it by installing the addon Personas Plus , clicking on its fox icon, then => Custom Persona => Edit … if you choose Apply, even you can install the theme on your pc just as it is, skipping the process of approval and sharing.

Finally I ventured to elaborate your image to better respond to your question and this is one possible between results


obtained by resizing it from 3000x200 to 800x200 px with the height value locked, then copying the result to the end from right to left.
I hope to have helped you

This helps a lot actually, thank you! Comparing yours to mine I can really see what you mean. I will definitely look out for this in the future!