It may sound odd, but there is a trick to getting a good photo of a sand sculpture.
First, clear clutter around and behind the sculpture. You don’t want that distracting from your work in your photos, or the photos that others take!
Most sand is white or off-white and in bright sun, this washes out the subtle details you have carved. And a white sand sculpture against a background of white sand? Pretty much looks like a white blur.
As the sun moves throughout the day, it will cast different shadows and change the appearance of your sculpture. Take photos throughout the day, later, you may find that it looks better in certain light than others.
If possible, wait for the sun to go behind a cloud. If it is a cloudless day, have someone capable hold an umbrella to completely envelope the sculpture in the shadow. I say “capable”, because a sudden gust of wind can carry it out of the hands of a child (or careless adult) right into your sculpture!
Gently deepen grooves around features and boundaries to increase contrast.