[Plugin: Recent Posts Slider] How to make just one column to have just image to fit 100% width

Hi there,
I’m trying to change the thumbnail image to fill whole width instead of sharing the width with except.
Here is screen capture what I’ve been done so far.
https://96.0.125.181/en/wp-content/uploads/screenshot_254.jpg
So, I make the image 645px wide – this is width that I want.
but the images are still just half of the size and just stretch to fill 645px.
I’ve trying pretty much everything with ‘recent-slider-post.php’ file and ‘style.css’ file,
but I can not figure out and frustrated ?? and finally decide to ask some help to everyone here.
Anyone has any idea how to make the image to fit with out stretched?
Please help me~
Thanks and regards.
Vic

https://www.ads-software.com/extend/plugins/recent-posts-slider/