Hi Sian,
From your screenshot I can tell that you didn’t filter your dynamic page to show a single item, it’s showing all items. I can tell because it says (All) in the name. So what’s happening is your page is filtering on all the items but you designed it to only show one, so it’s showing the first item each time.
You need to go to the settings for your dynamic page and add a filter to the URL that makes the page a dynamic item page. You need to filter on the field in your collection that uniquely identifies each entry.
I’ll send a link to some articles in a sec.
-Jeff