What you have gotten for advice so far is pretty much correct. When I got my first silicone neck seal many years ago, I was not told that I did not have to cut it down, so I went through the same process I had used on latex seals, cutting off a number of rings to make it fit. It worked just fine. Just be very careful about cutting it.
Today I would be more likely to just replace it, which I did when I got a hole like that (a little lower) a couple years ago.
So how did you get it? I'll tell my (embarrassing) story if you tell yours. I was staying in a motel room, and I had forgotten to bring my normal drysuit hanger. I had to use the motel's hanger, and it was one of those where the hanger just has a knob sticking out the top that slides into a slot in the hanger permanently attached to the rod. I was taking the drysuit down the morning of a dive, and as I attempted to take the drysuit off the hanger, it slipped out of my hand, and that little knob poked through the neck seal.