In Level 5-3, where do I use the final red key?

In Level 5-3, where do I use the final red key? - I Hate Nothing About You With Red Heart Light

I have an extra red key and have scoured the entire level for a red lock barrier, but cannot find it. What am I missing?

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In Level 5-3, where do I use the final red key? - A Woman Wearing Red Headscarf Using a Smartphone

Yoshi's Island (SNES): 5-3 (100 points)

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