What are you playing?

[Lemonray]

I remember Forest Temple being a NIGHTMARE

It wasn't much trouble for me, but I do remember how it's possible to completely miss one of the keys you need if you're not paying enough attention.

That would be the one inside the chest on a high-up tree branch, outside of the door leading into the temple. I think there's also a golden skulltula in that room, which I think was how I came to find the chest the first time I played the game.