What should the center do in this basketball situation?

I had a game a few days ago where we had the lead with 20 seconds left. We were playing a 2-3 zone and i was playing center. The other team ran down the clock and their PG managed to penetrate past our guards. I stepped up to help, but the PG passed to a wide open player under the basket and he scored the game winning layup. Was i wrong for stepping up? If so, what should have been done instead?guards. I stepped up to help, but the PG passed to a wide open player under the basket and he scored the game winning layup. Was i wrong for stepping up? If so, what should have been done instead?