Unless they've changed the locks the shower door key only fits the shower door. We got three black-headed keys with ours; one for the entry door, a second that fits the storage compartments, and the shower door key. Ours doesn't have the large front storage hatch, so maybe the newer ones have more keys.
It's not the smoothest lock in the world to get the key into, so maybe you have it and it's just not cooperating.
It's never too late to have a happy childhood!
Lee, WU0V, and Courtenay, N0ZDT
2011 Rockwood A128
2000 Silverado 1500 pickup
60W solar system
2000W inverter generator