Well, that is your problem then. The acrylic adhesive on the top side (your printed part) will stick very strongly even at room temperature or below. I am flabbergasted why anyone would suggest that stuff.

If your want to print in PETG I strongly advise to move to a glass bed and 3DLac (or the infamous brand of special hairspray if you live in the US). Works the best I have found for PLA/PETG/ABS so far and you get a mirror-smooth heatbed side which can work out really good for some parts. And as I said, when cooled down the parts just pop off.

You can also try Printrite (Printbite?) with which others have good experience. When cooling down the parts also pop off, and it also works on a range of plastics. Curious Aardvark has made a lengthy post on that stuff, just search for it on the forum here.