if anoyne has the same problem as me read this. to get back to the castle, howl in the grass and take the bird upstream. when you land look at your map. there is a river (2 torches at the entrance) that leads to hyrule fields. jump in the river.
okay when you get to hyrule you'll get to fight and activate a portal outside of town. go in go under the crates get the tear. then midna will say something about the last tear. teleport to the lake after that. then you fight the boss and get the tear.