Have you considered a liner brush, scripting brush or a grass brush. A splayed fan brush is always a fun one to play with as well.

You may find this interesting.

I agree with Keith a., I think you have a solid start, think of what you have done so far as an underpainting, start laying in thinner layers/lines of the other colors, browns, golds, tans, greens, reds and it will work out

Yes a fine brush helps, I use a wedge/angled brush or a dagger,
the edge when wet and wiped comes to a sharp flat edge I use it like a exacto knife would cut,leaving a really nice sharp lines.
here are a few examples.. you need t o add dark and lights to give it more depth, especially dark around the bottom along the water.. and add both mixed tones.
I add raw sienna/yellows and browns to my greens to give the grasses more tones. Black or burnt umber to sap green for the darks.
Hope this helps..best example I have .

this shows the grasses but not the colors as it does above

What an excellent thread! It gets to the heart of the matter and really informs with details about the equipment and how to use it, even showing examples. I’m sure many artist love a looser style, but how many have no way of finding out simple answers to their concerns? What a great site for new members like myself who have the time and desire to “lurk”! This is more rewarding to the viewing numbers (323 at this point for this post) that show in the side column who have opportunity to see how others have dealt with problems that they may have encountered. My only problem with it is that it seriously cut into my actual painting time….
Jon C.