Thanks for updating in! Please be advised that the recent post element will only display up to 4 items. In your case, please make use of two recent posts elements and display 3 items in each element. You can make use of the offset option to make sure that both elements will display 3 different items.
Excerpts or preview of the articles is not available in the recent posts element. You will have to modify the element before you can display it. And again, before you can modify the element, what you are trying to accomplish requires a template customization, we would highly to suggest that you use a child theme. This allows you to make code changes that won’t be overwritten when an X update is released. After your child theme is setup, please review how we recommend making template changes in Customization Best Practices.
After having to set up a child theme, you can then follow the suggestion from this thread: https://theme.co/apex/forum/t/recent-posts-shortcode-change-image-size-add-excerpt/1517/2
Hope this helps.