When scientists say the universe is expanding, they mean it is moving outwards from a perceived central point, almost as if from an explosion.
However, that doesn’t mean that more matter is being created in the universe, which you seem to imply. This would violate the Law of Conservation of Matter. The existing matter in the universe is simply expanding outwards (though expanding into what is unknown).
God isn’t necessarily creating more matter in the universe (though He certainly can, and has). If you mean “Creation” as the event by which our universe came into being through the creative action of God, then Creation has ended. If God created the universe from the beginning and “He saw that it was good”, then he has no reason to continue that Creation. If, on the other hand, you mean “Creation” as the introduction of more matter into the universe by the action of God, then yes, “creation” is continuing. However, though God’s Creation of the universe may have stopped, His saving action in the world certainly hasn’t. Salvation History has been happening since the dawn of time and is still occuring.
I’m not sure about Church teaching on this matter, but I believe the Church teaches that Creation took place as a discrete event, but that Salvation History is ongoing.