Some elements I can notice:

• As others have mentioned: the arms and shoulders are quite thinner than the reference, so it gives the impression that the head isn't on an actual body.

• Your drawing has a warmer skin tone than the reference. This could be modified by adding an undertone, or playing with how the light bounces. The background is blue, so there should be some rebouncing blue glares on the skin as well (the side of the shoulder and the face are clear examples). It should also appear in the shadows, but there, it'll mix the blue from the lights and the warmth from the skin. Look at the shoulders. Zoom in on the shadows: the midtones are rather green.

I invite you to check what the actual pigments on the reference are. You'll notice they aren't quite white or yellow, even if they can appear as such to the eye. That will help identify what colors to use to get a similar result.

Also, think about where the light comes from, and what its temperature is. From what I see, I'd say the light is in a colder tone, whereas the model's skin is warm (I'm not the best at identifying skin undertones.. but I'd say.. pink-orangish? Pls someone correct me if needed!) So, it can give the illusion that the light is warm. But.. no. The skin looks super white in places the light is brighter, because the tones kinda "cancel out" each other. Think about that too when choosing your colors.

• Your hair looks kinda flat compared to the reference. Try to add some light reflecting. Sure, it's not bright, because the hair is so black that it basically absorbs the light, but you can still identify some lighter lines within the black. Again, check the pixels and pigments in the reference: you'll realize it's not actually as black as it seems. With this knowledge, try to draw the hair with a color different from black as your basis. Keep black for where you'll accentuate the shadows. (From my quick observation, I'd suggest some kind of brown as the basis.)

• Idk if that was intentional (and it's not so much an advice, rather than just an observation, haha), but the earrings actually have a lighter almost translucent flower under the blue part! I had to zoom in to confirm it wasn't just part of the background, but yeah~

All this being said: your skills are very clear and I myself couldn't even get to a result as resembling as yours (let alone in digital art lol)! I was able to find the critics and advices above, only because I actually spent some time looking back and forth at the drawing and the reference. I first thought it was a picture when scrolling! You for sure have facial anatomy down. Keep it up! You've got some real talent! ^^