That is okay. The only way that the damage would work is if your opponent had only 30hp left. A hand trick to point out (thanks to my wife pointing it out) is to then play a card that makes you opponent discard some cards in their hand. That way you could blow the defending Pokemon and cards back into you opponent's hand and next turn hopefully have some of them discarded. That'd be a blow to your opponent.
:-D Evil but fun!