Dariusz,

I see you have posted this on a couple of other sites so I will reply here.
Hybrid canna seedlings often do not resemble the pod parent. I wish you had given a complete photo of the entire blooming head.
My first impression was simply a wilted flower bloom. I think all canna cultivar blooms exhibit wilted blossoms if the stem is cut. The same can be said for any bloom that has completed its bloom cycle. This may not be the case for your seedling but if it never holds an open blossom it may not be worth saving. Many of the orchid flowering cultivars are somewhat night flowering and the blooms quickly wilt in the mornings making them less useful in the horticultural marketplace.

Kent