On Factorium, in the green gem cave I got a key, which I used in the same..

On Factorium, in the green gem cave I got a key, which I used in the same cave to get to the gold stash. Now I don't have a key left to open the door to the starting to pick up a block to open the gate to continue. So I backtracked through the water area to pick up the block by the red lasers and switch. Carried the block to where I was, the gate dropped, but now there is no white square to drop resources to continue forward. I feel like I shouldn't have used that last key for the gold stash, but for the door to the main area. Am I stuck?

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