Broken post grid lay-out

#1 - I have created a grid layout with 3 columns and 5 custom post types to display. The first row shows 3 items and the second row 2 items, but they are centered beneath the first row. How can I fix this?

#2 - I have checked 'First images from content' as media source, but in my post grid I see also a featured image (which does not exists) and an empty thumbnail image. How can I fix this?