Full-width Portfolio has strange left margin and what image size to use?

hi
for some reason the portfolio does not appear to be in full 100% but instead there is some sort of a margain on the left side
you can see an example in this link: https://seowho.co.il/boldial/home-portfolio/
also, do the pictures in the portfolio need to be in certain dimensions or any dimension will work fine?
thank you
ethan