He lets Viktor arrange him just so on the bed, because it's a weird weak spot in his poor opinion of himself-- if Viktor is making him look a certain way, Viktor's ability to perform miracles outweighs his own self-consciousness. He's pretty sure he looks good right now, even though all the credit for that in his brain goes to Viktor.

"I don't want to ruin it," it's a bit of protest, and it would maybe reek of nervousness to hurt something that nice, but the tone and the way he rubs at the fabric, a little worried, more shows how much he wants the scarf, wants to get to wear it. He's feeling the sort of uncomfortable pull of having done too much today outside of his comfort zone, having admitted to too much, embarrassment and worry right at his heels. He can't stretch any farther-- but Viktor can probably read the flush on his cheeks at the question as permission, at least, if not desire.

Desire has to be somewhat obliquely inferred as well, though from a different language,

"It's your reward. You can have what you want," it's almost snappish, but there's enough ease in Yuuri's posture to keep it permissive.