PETG sticks to anything if the starting Z axis offset (gap between nozzle and bed when it is at Z0 is within the proper parameters. I use to print on heated glass, and removing the print was the issue, it ripped a chunk of glass out of the bed. PEI is what I use for PETG and lower my bed temp to 65C and still have issue with the print ripping up the PEI. I have started to set my Z offset to .03 higher than it should be.
Sorry I can not explain how you fix your printer just trying to convey that having PETG stick should not be a problem.
I would assume you have cleaned your bed with alcohol.
BTW you may want to look into Prusa slicer as it is one of the best maintained free slicers.