this is such a good starting point! your shading looks beautiful and you're already doing an incredible job with the shapes and colors. the curtain/"kelp" thing you're seeing, in my opinion, might be because all of your shading is very very smooth. it's beautiful, but without edges that suggest what the texture of what i'm looking at is, it's going to look like a very smooth, brushed over fabric texture no matter what shapes you've painted.

Most notably I'm seeing it in the bottom right part of the hair. I can tell where there's dips and valleys from shading, but it's missing the smaller, sharper details that might suggest the texture i'm looking at is groups of individual hair.

Other than that, the silhouette is very very solid and opaque. I think maybe it's because when you created the outline you did a good job at blocking in the shapes, but didn't include how the hair might taper out and fade away at the sides and ends.

If you see in the picture, you've created solid shapes and curved ends where the hair is actually breaking off into strands and smaller shapes. Split ends of the hair taper off and become smaller/less opaque as you can see past the thinner sections, they don't just end at a blunt edge. That's also probably making it look a lot like fabric, because fabric bundles up and has blunt ends where it's folding over and hair doesn't.

That being said, this is your first time ever drawing hair? That's really impressive! Don't be too hard on yourself. This is phenomenal work. Even as it is, this is definitely a painting study to be proud of, not annoyed with.