Hello
You can add new module position by copying the same code of these module position as defined in the spotlight.php files ,
Here is documentation to how to create module position .
But if you are adding 3 more module position in the same row , in this case you need to decrease the span size for the module position(2X6=12) , as in Boootstrap total width of the container is span12 . as per your screenshot now 6 module position using span2 for each one , if you will add more module position you need to set some module position size span1 , simply total size should be span12 .
Hope it help.