Be honest with her.

"Listen", you whisper, and she is bending over the pool edge, close to you. "Lena, listen...I got a little problem down there." You're closing your eyes. Can't believe you've just said that. "Oh, that's it!" she responds in a normal volume. "You've got a hard one!" she smiles, relieved. "But that's not a problem, you know? Boners are common here too, can't always control it!" And she reaches you her hand, wanting to get you out. You're shaking your head embarrassed.

"Lena, listen!" you whiz. "It's not only that! My dick is just...REALLY...small." Your head must be close to exploding, red like a tomato now. Lena stares into the water surprised, trying to catch a view on your little manhood. "What do you mean, really small?" she asks you calmly, now looking REALLY interested. "It's like...that." and your fingers show her a length of 5 centimetres. "What the fuck", she mumbles fascinated. "Please...help me, Lena", you beg her. She smirks at you.

"Ok, little chubby one!" she says, grabbing her towel and handing it to you. Now that dangerous moment comes - you're pushing your body up, and pushing yourself out of the water, now lying on the edge of the pool with your back upwards. The girls behind you giggle, as you're exposing your big butt, going full moon right now. Embarrassed, you're quickly covering your naked buttcheeks with the towel, and wrap it around your body. "Thank you so much, Lena", you mumble. "Whatever you want, I'll do anything for you!"

She smiles. "I deserve to see it at least, I think!"