That's a small yellow. I've seen them not grow, especially in Poplar areas, and being you broke the mycellium, there's a good chance that's all it's gonna do. Can always tell the Polar Yellows from the Elm, Apple, Ash Yellows, as their "pits" take on a more elongated, or oval appearance.
I always called them poplar morels. The ones I have found around poplars in my area never get much bigger than that. I have left them go for a week or more in ideal conditions and they get about 3-4 inches and thats it. Good eating though non the less!!