Brew comes out acidic, what am ı doing wrong?

Just did my cold brew coffe, full immersion in a mason jar for 16h, used a dark roast, grinded my self (used a "essresso mixture" 100% arabica, used the coffe ı use for mokapot) grinded to a corse grind (around to a french press grind). Used strecth film the seal the jar and steeped in the fridge then used coffe filter paper to filter it.

İt tasted acidic not bitter, bitternes was perfect.

What can ı do to fix this issue.