Without seeing the content of the workbook and only seeing your screenshot I think Tableau did it's best;) You have 3 "outliers" Left- upper, Left-lower and Right-lower side and Tableau "renders" your map based on the "outer side" of your datapoints. You can "play around" with the map by excluding the outliers.
Hope it's clear.
Hello Norbert, thanks again for replying my question . Is there any way that I still keep the outliers and customize to fix the size of the map to get a default bigger one?