How would you like it to be?
Woohoo, thanks! What did I win? 
Massive respect!
And the approbation of your peers.
My preference would be only positive points for correct picks, but the obvious flaw there would be it would encourage picking long shot upsets.
My second choice would be to award 2 points for correct picks, while subtracting one for incorrect picks. There’s probably an obvious flaw there too, but I don’t see it at the moment.
Doesn’t really matter as the system you’ve devised is working fine.