Maciek -

I see that the strap flattens and adapts to the shape of the watch at the ends.

I would add more "helper" profiles that mimic the watch profile (top view) to try to force the loft to conform as needed.

Because "History" is enabled for Loft, you can move and resize your profile curves while watching the Loft automatically update.

This is a tedious method to be sure, but as Michael stated, it's more of an organic shape not easily made in NURBs.

Ed Ferguson