@Mary-Toth First off, I think you're being a bit too hard on yourself :). It probably looks better than you think it does (considering we're always our own worst critics). I think it looks quite nice as well.
I do agree, traditional media is a lot tougher to change. I think that's especially true with water color. That's one of the reasons I've gravitated towards acrylic when I paint traditionally; if I don't like it, I can literally paint over the entire canvas or the section I want to completely redo lol. The only reason I hate working with oils is I have no patience for it to dry
I think on this piece here, if I were to say something is bothering me, I think it's the stark black against the clouds. It's really abrupt and it sort of tears away from how that kind of environment would react. Assuming this is a stormy night, I think the entire background would be significantly darker where the lightning was illuminating the edges of the clouds it could light up.
One of the best tips I remember getting for general purpose on back/middle/foreground was keep your value ranges tight. So for example the back range would be dark, and vary slightly, but be dark all around. Your mid would a narrow window of varying mid-range values and your character/focal point would your highest contrast ratio.
The waves and the boat are super great. They look really nice and stylized. I just think the background needs some way separate into it's own value range.
One thing I do with my acrylic paintings is I take a picture of it on my iPad, then pull the photo into Procreate and I'll paint over the areas I'm not happy with a hard brush to get a sense of what feels better. You could do that or just pull this scan into a painting program and try it (if you haven't bought anything yet, just use Autodesk Sketch even which is free and pretty dang good for a free app).