As advice by all, here I modified it...the base of the pot is pure sphagnum to keep some water in the pot, side is purely pebbles, center where the campanulata is sitting were a mix of 50 sphagnum 50 pebbles, topping with full sphagnum
Temporarily cover 90% of it with this transparent cup to increase humidity
was surprised that the pebbles inside the pot were wet when I repot it about an hour ago as the last time I watered it was yesterday...