Welcome to the forum. I wish you luck with that NPXL, but I'm not that hopeful, based on my own Benjamin experience. Best to see if you can find a local airgunner with a lot of springer experience to help you out.
.25 cal. is hard to find pellets for locally. It's gonna be tough. I'd start with a tin of Benjamin Premier domed pellets and then something on the light end of JSBs line-up. Maybe a sampler pack from pyramydair.com or straightshooters.com. Once you find a pellet it likes, it gets a LOT easier.
Also, read up on how to hold them. You can't be really firm all around, like you would with a powderburner. It varies from gun to gun and person to person, but these Benjamin magnum springers generally like a medium firm hold in the shoulder, a light grip with the trigger hand, and a soft, movable support under the forestock; beanbags or something. Lots of us also rest the back of our hand on something hard, then rest the gun on our open or semi-open palm.
As I said in the other thread, check your stock screws and your scope mounting screws and your trigger guard screw(s).
Move back to 10 yards, to start.