Grid of Post Thumbnails Above Normal Post Layout

Hey everyone,

I’m looking to create a 1×3 grid (one line of 3 thumbnails) above my normal post layout, and I’ve basically got it there but its duplicates of the posts under it. I was hoping it would be

3 latest posts in thumbnails
next post
next post
etc.

https://format1.iheartargyle.com/?cat=5

I have this solution plugged in right now:
https://return-true.com/2010/05/creating-a-post-thumbnail-grid-in-wordpress/

I’m guessing I need it to be one seamless loop?