She will knock on the door and ask

Not entirely thinking clearly, and slightly in a panic, Sophia shot back up and rushed over to the door. Still fully nude, she stood in front of the stall, crossing her legs awkwardly and covering her breasts. She knocked on the door and spoke:

"Uhm sorry, I dropped my key and I think it's in your stall. Could you hand it back?"

"Let me see." The voice on the other side sounded. It seemed to be a guy about her age, unfortunately. "Ah, here it is."

A fraction of a second later, she could see the lock on the door shift from red to green. Sophia began to protest, but it was already too late. The door swung open inwards, and there was nothing she could do to stop it now. Before she knew it she stood face-to-face with the guy. She had not expected him to be dressed already, but it's safe to say he was far more surprised with what he saw. He looked in bewilderment at Sophia, who covered herself the best she could. She turned bright red as she felt him stare at her nude body for what felt like a good 10 seconds, but what in reality was nothing more than a split-second, before she snapped out of it with a shriek and dashed into an adjacent stall.

"Uhh, do you still want your key?" The guy said, bewildered.

Sophia stood shaking in her stall, buring her face in her hands. How much had he seen? She had covered her nipples, but everything else was right in the open. She had to get her key now!

"Yes, of course!" she answered.

A few seconds later the key slid under her door.

"Thank you..."

"No problem at all.", he said curiously, "Will you be OK now?"

"Yes! Thank you!"

Sophia bent down to pick up her key, and saw the legs of the guy still outside her stall. Perhaps he wanted another look, but she was not about to give it to him. This middle row of stalls each had a door on both sides, so she deftly retreated through the opposite one. She found herself once again out in the open, but she could quickly retreat to her original stall and put her bikini back on.

In her embarrassed haste to get away from the guy, she had forgotten to check this corridor for people. Luckily, it seemed she was right on time. She could just see the cleaning lady turn the corner with a few trashbags into the room with the lockers, back on her way to the reception area. More pressing were the people behind her, who were coming from the showers towards her. Sofia quickly ran back to her original stall.