How much do you think does a N&F super guy widen in the butt area?

I just got my first selvedge denim (N&F Kimono Print Super Guy) and while trying it on everything felt fine, sure it is a tighter fit but nothing uncomfortable. So I wore it again today and during sitting most of the day I noticed that it got really uncomfortable. It felt like I was clenching my butt muscles the whole time, the jeans must be too tight around the butt when sitting.

Will it widen in that area with time or am I better off selling them (since they can't be returned anymore)?