Hi all, got my new kit, the Flying V bass, and started putting together my first guitar. Measured and placed the bridge, put the neck into the body and drilled/screwed it in. It was a tight fit, and have checked since. It’s in there well. Then I placed in the tuning pegs and strung the bass. The action is really high. I dropped the bridge saddles. As Far As They Go, but still it is real off. This is when I took the neck off and inspected. Put everything back on, and checked the curve of neck. It seems straight/ meaning no concave or convex. I let sit and strung for 24 hours, but no noticeable difference. The nut seems to be fine- action is good at top/head of the neck, yet high at the bottom by the body.
I’m not sure what do do here. Did I get a bad neck or body? Should I start sanding the body neck slot to try and modify the angle of the neck and body placement?

FYI- although this is my first “build”, I have been playing for 30+ years and have plenty of neck adjustments, replacements, body/pickup/headstock, FrankenGuitar modifications.