RE: drill slipped while mounting wing
If that's the way the plans/kit call for it It most likely is fine, But I'd at least add some extra gussets to the sides of the block,, not just at the bottom. The further that bolt hole get away from the side, the more torque is being applied to it. Allot depends on you're flying style too, I'm a pretty aggressive flyer, so I like to have thing extra strong when ever possible
good luck