With every thing else thats wrong with that panel , the back fed breaker being properly secured is the least of the concerns

It never ceases to amaze me the effort some people put into doing a project incorrectly, when doing it correctly would be easier!

Why not just use an offset nipple out of the 1/2" ko ,under that receptacle, and go into a surface mounted weather proof box ? Seems like that would have been easier then cutting out the side of the panel.