So, take a look at the original picture. The problem here is the original image has certain aspects that are out of focus: the background and some of subject. In your piece, her (the subject) arms are blurry for no reason, because the background is very clear. However, for the background to be clear and for her to be blurry, more of her would have to be out of focus. What we see in the original is an example of "depth of field", which your design outright ignores. Hard rules on how photography works aren't always things you must follow while doing this kind of stuff. However, as you can see here, not doing so can give you a weird result if you aren't careful.
Since the original image appears to take place in real, three-dimensional space, we see the effects of things like aperture, focal length and distance creating the depth that exists in real life. Look at your screen and notice how everything beyond it is now slightly blurry on the edges of your vision. Look beyond your monitor and notice how the screen is now slightly blurry. A camera lens can replicate this, and we see it at work in the original image.
This is a good example of how picking good images to render is very important. You want to pick an image that has crisp lines to cut out, and tends to be very flat. You don't want your render to be partially out of focus, otherwise you'll run into the problems you have here. With experience that will matter less, because you'll know how to blend things better. Such as adding feathering or blur to images manually to make things blend better, or intentionally creating depth of field to blend that some part of your render is also out of focus, and some
other tricks (lightning, shadows, smearing, covering up, to name a few--
@Fruit is good at this).
Your selection of the arm is too fuzzy and feathered, so it looks awkward. Your selection of the nose and face is too crisp, so it lacks depth on the crisp background. The face is less of an issue, because you can just have a stylized image where the depth doesn't really matter. However, that arm is very distracting.
Next, I want to talk about that pattern you've dropped down. It appears as though you just dropped it down and likely set some blending mode. I highly suggest being more creative than that. Anyone can just drop a pattern down and change the blending mode. Take the time to do something interesting with it. Even if it's just isolating it to one section of the image, such as her skin, while also masking out her eyes and lips.
I will applaud you for getting rid of that watermark though. If you would have left that in, I'd have to create a wall of shame. lol