I know this info is late for you, but this mod isn't calamity supported. There is another one that is made specifically for calamity, although I heard it may be broken with Calamity's current update. Both this mod and the calamity version (Terraria Ball Super) are getting full new builds and hope to be release this year (no promises from the mod creators).

Additionally, the dragon balls will spawn duplicates if the ball is put into a storage chest. The only way to avoid finding dups is to always keep them on your character.

do you have them in your inventory or in a chest? from my experience putting them in a chest was cause duplicates to be found

One of the newer updates removed that.
You can still find duplicates if you come across them in the world, obviously because its support for multiplayer.