“Did I remove enough” can be resolved by covering the surface to be cut with a thin layer of sharpie or similar marker. Once the marker is gone the entire surface has been cut. The entire cut surface being square to the steer tube is a function of proper use of the cutter.
Without an indicator or known square ended tube there isn’t a great way to check and get a numeric value.
In theory you mount the upper headset then rig a scribe from there to the crown race seat, but that’s full of opportunity for error.
I’m with the above suggestion. Try to drive it home and then see if the headset adjusts properly.