How to improve your photo
You failed to mention the speed. It's not fundamental and I can see that you know what you're doing but still, the most information I get the better I can help. Also, and this is very important for me, you're not saying anything about the film used, the ISO you shot and development details.
There is some strange effect on the line that separates the sand from the sky and the sand has a type of saturation that feels not very consistent with the sky. Did you add sharpening to this after scanned? Or, did you darkened the sky a bit? There is something there that doesn't feel right to me and makes this look like a montage. If it is a montage it's OK, but still, this is ambiguous... I like ambiguity but sometimes it's just strange and feels their might be something wrong.
The foreground defocus is a good way to force the viewer to go forward and imagine what is beyond the dune but as I see it this is not defocused enough to relay the viewer into the background. It starts by feeling the focus is in the wrong place. I would use it at f2.8 for the decreased DoF. When having the foreground defocused enough one thinks it's made on purpose, but if the area you want to bring out of focus, in order to select what is in focus, is still close to focus, then it looks like it could be a mistake and the objective of leading the viewer to the background sand is not so effective.
I don't mind this sort of ambiguity but for it to work it would need to be consistent with other examples on a show. This is clearly aimed at Fine Art Photography.