Insufficient or too shallow Depth of Field is due to TOO LARGE an aperture.... NOT "too small".
That's a common mis-statement, because the lower f-stop number = larger aperture. The thing to remember is that an f-stop is actually a fraction: "f/x" or "focal length divided by a denominator". So the larger the denominator, the smaller the aperture (and the deeper DoF will be). We tend to make it worse by often writing "f2.8" instead of "f/2.8" (for example).
Can't tell what f-stop you used, since the EXIF has been stripped off the image (which bothers me!
) I was looking for the EXIF to see what shutter speed was used... Because if it was relatively slow, even a slight breeze might have cause some of the blurring due to subject movement.
This shot would have been a good candidate for "focus stacking". It might be difficult or impossible to shoot just using small apertures. You might never find enough DoF. In fact, a super small aperture that increased DoF, might well mean loss of fine detail to diffraction.
The aspect ratio of the image doesn't bother me at all. In fact, to me it just seems appropriate.
Not a fan of heavy vignetting, though I often do some subtle burning in on image edges and corners.
Something else "bothersome" might be the background. It's strongly blurred (would have been less so if a smaller aperture were used), but still rather "busy". Might have been interesting to see how it would look with a plainer background. I've used colored cloth or poster boards as backdrops at times, to make a delicate subject like this stand out better.
Just for example:
For this image I used a cloth backdrop that happened to be a close match to the colors of the flower...
For this I used a black velvet backdrop...
But that's not always necessary. Here using a 500mm lens that's unusually close focusing very strongly blurred down a fence and woodpile roughly 15 or 20 feet behind the flower...