Bounce is what happened. Paint literally bounced off the wing and onto the fuselage then hardened. Next time try shooting the joins of wing/fuse and elevator/fuse first and make sure to get a band of coverage well along on both sides of the join; then when you spray the wing or fuselage shoot away from the join. Low air pressure helps eliminate this along with low paint flow.
You can sand it out but don't start any coarser than 1000 grit, do it wet as well. If you're careful and only sand off the excess paint you shouldn't need a fresh coat of black under it.