I think that looks more like hemianthus glomeritus. Leaves look much to big to be HM.
Tank is looking nice. Not what I've typically seen with a lot of iwagumi tanks. A lot more variety in flora, but still looks good. I think the variety in flora brings a bit of a different feel to it than the minimalistic iwagumi with a carpet and a background plant. It's different, but I like what you've done with it. It seems to work pretty well with your hardscape.
I do think your early concerns about the size of the stargrass might have been valid. It does look rather large in this small a tank. Maybe something with finer leaves would look good in that spot.
How did you do your trimming? Did you pull it all up and replant the tops or did you take off the tops? It almost looks to nice and neat for just cutting off the tops, at least neater than when I top my stems. It usually takes it a couple days for it to start looking good again after a big trim.