Having trouble adding new vertices to a polyshape

I'm using Probuilder and I'm trying to add more vertices to a shape after I've edited it. I click "edit Poly Shape" and it reverts the shape to the original size. Is there a way to avoid this? I'm watching a tutorial by Gabriel and he does it without issue.

 

I misunderstood the tool. I was clicking off the tool during my initial edit and transforming instead of using the tool to make edits to the poly shape. The behavior makes sense to me now.