Use this trick to get both the fish trap and small trap without wasting items. After getting the necessary materials (basket and twig), make a small trap. Place it at either of the areas used to drink from the river. Place it near the middle. Go onto the grass and walk towards it, and do not stop before pressing A. As soon as the thought bubble saying small trap appears, press A. You should be using the fish trap. If you would rather use it as a small trap, go up to it, press A, and use it normally.