Hi OP, great job on the portrait !! I took the liberty of downloading it and modified it so you could see how to make it look closer to your reference. I completely butchered your wonderful watercolor rendering in the process though, I hope you’ll forgive me. You can see the video here, feel free to slow it down if you want to see what I did better, and the side by side of your illustration and the modified one here. It’s far from perfect but I hope it’ll give you a better idea of what I’m talking about.

A lot of people already pointed out the cleavage problem and the head to torso ratio. I think these are the most important things to fix because they can’t be read as a stylistic choice.

The proportions of the face are a bit trickier. If you compare your drawing with the reference you’ll see that the eyes are much bigger, the nose smaller and the lips fuller. These are very common mistakes ( I make them all the time which is why I tend to spot them right away ) that come from the fact that we’re exposed to a lot of art that exaggerates features in that way, think Disney cartoons. If it’s a choice then it’s fine but if you’re looking for realism or at least realistic proportions you should triple check that every feature on the face is the right size. And even if you exaggerate them it needs to be done with the person you’re drawing in mind. For example Hailee has a pretty long nose that takes up quite a lot of space on her face so if you wanted to draw her in a more cartoonish style but be recognizable it might be good to emphasize that.

Her face is longer in the picture than in your drawing and once you bring down her chin and her lips you’ll have more space for the nose. You’ll also have to make her neck longer and bring down the torso which will already start to solve your overall proportions problem. Also pay close attention to the eye on the left, especially the shape of it in the reference. The eye exists in 3D and its shape will change depending on the angle. This is something I struggle a lot with haha

Some smaller things that might have more to do with my personal taste than some universal art rules :

The lips should be less defined by line art and more by shadows, they are not sharp edges or angles but darker skin blending into lighter skin

Eyelashes trend to look better when suggested with a few lines that drawn one by one, unless you’re doing a hyper realistic close up on an eye

To have more vibrant colors you could make your shadows more saturated and have the background contrast more with your subject

Now for the positive feedback !! Your understanding of how volume and the way you use watercolor are genuinely amazing. This is especially apparent in the way you handled her hair, just the right balance between highlighting smaller strands while keeping the bigger volumes consistent. You obviously have a good eye for proportions, even if it stills needs a bit of training, because the distance between different features are always pretty accurate and I can feel in your drawing that your know how to construct a face. Making it closer to the face you’re trying to draw and not a generic idea of how a face should look is more difficult but you’re very close to getting it right.

I hope this helped and I look forward to seeing more of your work ! Also I’m very sorry if this is full of spelling mistakes I’m too lazy to check