The leash is what ties you to your board, so you definitely want to attach it properly.
You'll need :
Remove the cord attached to the Velcro rail saver on your leash and slide the loop end through the D-RING located at the tail of your board.
Pass the knotted end of the cord through the loop end.
Place the knotted end of the cord inside the fold of the Velcro of the leash rail saver.
Fold the two Velcro layers one on top of the other to secure the cord in place.