I trim my cover so the edge has all bubbles but with the 12 mil and even the 8 mil, it isn't very easy to pop the bubbles. The cover is much thicker than bubble wrap.

Everyone has a technique for trimming but the one I found to be easiest is lay the cover over the pool so the cover is stretched over the coping to the water at about a 45 degree angle. I leave it there for a couple of days until the folds settle out. You can then take scissors and cut along the coping edge. Because of the 45 degree angle, the cover should then fall to the water level near the tile. Having a small gap between the cover and tile is not a big deal so don't worry too much about getting it perfect.