If you can enter the castle you should have everything you need to complete it.
The sparkles in the right room are meant as a indicator for the key.
An the sparkles in the left room are meant as a hint that you can interact with the pile of wood next to the sparkle to push it down to create a new path. I think that may be what you are been missing to progress?
I hope this helps^^
If not feel fee to ask again!