You see two issues here I suppose: A) an uneven print bed (many suffer from that) - solution: Pick the tightest bed leveling pattern you can or even go to 11x11 via GCode. More on that here: Bed Leveling - Revisited & Detailed
B) PETG has a tendency to warp, and that may cause the nozzle to catch a warped part of the print and dislodge the print sheet. My solution was this: Magnetic print sheet fixation - #10 by Hauke