What am I doing wrong?

I am staining my friends guitar fret board. It's white with few but deep long grains. It is probably a super cheap wood my guess is pine. I removed the old stain and sanded it down to 80-grit. After six or seven coats I decided I wanted it a lot smoother. So I figured I could do two coats then sand with 150-grit. Then two more coats with a 220-grit. Finally two more coats and finish it with 330-grit. However after my first attempt to sand it with 150-grit nearly all the stain came right off. Almost in like a waxy goop. I always wipe of any excess stain with a dry cloth but I guess it just had way to much build up. If someone could give me exact instructions that would make my day.