pink flower

You asked, . . .

"any ideas on how to improve with a prime lens"

I noted from your EXIF data in the Details tab that you shot this at ISO 200, Shutter Speed of 1/4000 and I think the Aperture was at either 1.4 or 1.8.

So, even hand-held you could have lowered the ISO, would have still maintained a higher shutter speed and most all lenses have whats called a "sweet spot" that is usually a stop or two smaller than it's maximum aperture opening. Something one has to experiment with!

I would recommend as a starting point using an aperture of f/2.8 to f/4.0 as a start.

For the shot you have here, . . . the separation between your subject and background is good which helps to give that creamy or blurry background which is desirable to make the subject flower pop!

When composing your shot, . . watch for things like the tall grasses just behind your subject flower. As you can see, they are distracting from the main subject.

Research your Camera or Lens User's Manual to determine its closest focusing distance which can be a big help when you don't have a dedicated "Macro" lens and are trying to shoot Flowers and the like.

Hope that helps some!

Keep shooting and posting!