By default, Get items only returns the first 100 items. In your case you should do two things since you have more than 5000 items.
Set Top Count to 5000. This will return the first 5000 items.
Go into Settings and turn on Pagination, then set a Threshold to something greater than the number of items you expect to have over the next few years. If you have around 6000 items in your list and expect there to be around 10000 items within the next few years, then set the Threshold to 15000 (as an example). When you set Pagination on, it will return the Top Count in batches. So if your Top Count is 5000, it will return the first 5000, then the next 5000, and so on until all items are returned or it reaches your Threshold.
