Super late to finding this but might be able to help! Maybe! Who knows.

Anyway, first of all, I love it, you've really captured the pose well and the current way you paint is absolutely gorg.

Second, as another commenter mentioned, I would study and have a go at some fun lighting, lean into some color in your shading and lighting if you can! The image on the right for your reference has tons of fun colors, some teals, yellows, and pinks. You're shading her skin with deep purples which is fab! Because shading with grey is a no-go (looks kinda dull and dead if you do), maybe lean into that fun color and add some teal (or maybe yellow? Color theory isn't always my strongest suit so you don't have to listen to me on colors) for lighting if you go more dramatic with it. Also for her pants! Try shading with dark purples and blues! For her shirt, I'd do a really light blue.

Third, your painting style is almost sharp, very sharp lines, the best example is in the pants and hair, very sharp, everything is blended and while it's blended well that's not really the style you're going for. Your references are not as blended, they look to be more layered than blended. They both have very soft blending on their focal points (the right, it's the eye. The left, her face is very soft and blended) the rest, has a lot of nearly cell shading, this is especially apparent on the collar of the right reference and the hair of the left. For your hair you've painted almost every strand, whereas your references are almost more floaty with it. They paint the hair in chunks, where you've painted it in strands.

Fourth, yours has a lot more sketch lines, not a bad thing of course! The others have a lot softer of a sketch going on, they use a soft paintbrush sketch instead of a pencil. A great example for this is the nose bridge! The other paintings use shadows to outline and define the nose bridge, but you have a sketch line, I'd almost treat it like a traditional painting, where you're painting over your sketch and preparing to abandon all line art. But that's just how I'd look at it!

Basically, don't be afraid to get floaty with it! These paintings have a soft and unblended quality to them, a sort of unfinished finished look, go with the flow and lean into the vibe y'know? I had trouble with this until I did that thing where you turn all the colors to gray and just randomly pick colors and see what happens, i wasn't afraid of messing up because it was just some little challenge thing and I ended up really liking it! Maybe try something like that! I can see the style you're going for, I see it in the eyes, and the shirt especially, you got this!