welcome Nick and great looking kit you scored. Even better being a school project. I've built one of these kits and love the axe. Keep sanding until you can rub your hands all over the body and not feel anything but smoothness and no bumps or dents. No need to go past 320 grit or the stain won't take as well.
Should look awesome in DT black stump.
Maybe if you can please post some close up pics of any areas you may think may be a problem