If the pudding is cooled down to room temperature and still runny, it may mean it wasn't cooked long enough. Try returning to low heat and simmering another 5-7 minutes while stirring, and cool again. Pudding thickens more as it cools, and even more when refrigerated, so be patient! Make sure the correct rice is used as called for in this recipe, different varieties of rice need different amounts of liquid to cook.