Quick question about Paypal and PSN purchases

So I have around $6 in my Paypal account, and I went to purchase Infamous: Second Son. When I bought the game, it charged the card connected to my Paypal the full price of the game, instead of taking the $6 from my Paypal account, and charging my card the rest. Is there a way I can use the Paypal balance before using my card? Thanks!