I have created a this recipe but I want to work in the player's inventory not just a crafting table since it is a 2x2 recipe.

 

GameRegistry.addRecipe(new ItemStack(ModBlocks.condensedpoppydust), new Object[]{"   ","DD ","DD ", 'D', ModItems.itempoppydust});

 

You have unnecessary spaces in the strings defining your recipe. For it to fit in a 2x2 square, define it using 2 strings of 2 characters each, rather than 3 of 3.