Why is my website's desktop layout too big?

Hi, my website’s homepage looks fine in a mobile format but when I view it on a desktop all the images are way too big and content isn’t in the centre. This is only on the homepage, my product page looks good. I have looked at a bunch of forums which recommend to paste certain things into the code to fix this, none of the dozen different code changes i’ve tried have done anything (I backtracked after and left things how they were). I’ve tried formatting the images to the correct file type and sizing them correctly, no effect. Anyone have any idea?