Insert an opening pick into the heated edge of the phone, between the plastic frame and the display.

The pick should slide underneath the plastic and remain above the copper colored shielding.

If you can see the pick through front glass, the pick is riding on top of the display panel. Pull the pick out, angle it so that the point aims more towards the plastic frame side, and try again.

Keep in mind that the display cable threads through the midframe just above the midpoint of the right edge. It may interfere with your cutting if the pick is too deep.