Hey there and welcome to the Community, @reyiyeb 
The new posts don’t appear in the widget right away because of the cache. Our widget actually uses a cache system to make everything load faster and reduce the server load. So the posts are updated every 48 hours.
You can read more about cache here: Why new posts don’t show up in my Instagram Feed widget
We also have a Wishlist request for a faster update period and you can upvote it here - Remove or reduce cache time.
Please let me know if this explains things or if you have any questions left 