Hey Trailrunner- You are correct, I did buy a Medium.
It was on sale and the only size left. I was in a hurry and thought
it would fit. Obviously I paid for my mistake.

I believe it's too small because it's riding on my shoulders. I did a
approximately 2 mile hike with little weight and it was already hurting my shoulders. To be fair to the pack however, I did workout my shoulders
in the weightroom the day before.

But again, I did measure my torso using from the designated instructions for various websites (gregory, REI). I measured 3 times, Got 21.5, 20, 20.