For sewing stretchy fabrics my advice is to purchase an overlocker not a sewing machine, sewing machines will generally suck at stitching stretchy fabrics. If all you have is a sewing machine I recommend triple stitching if your machine has that as a setting.
I’m not a professional at this, I just repair my family’s clothes so if I’m wrong feel free to correct me.
I’m definitely not a printing expert but it looks like you’re under extruding, is the extruder the same size as the old one or is there some other change like that? I say this because the bottom layers look better than the higher ones, from memory cura over extrudes for the first few layers to help with bed adhesion.