What do you mean by fine? If it looks like small grains, a re-spin may solve the problem. If it doesn't, try letting it warm up slightly and re-spin it. But it may be that the fat-protein-sugar balance isn't right, as the previous answer suggests.

They recommend 24h, but 20 should be ok-ish….
Depends how you made the ice cream. If you’re using milk only, then you’ll need a thickening agent (Xanthan Gum, Egg Yolk, Collagen, etc).