I would say this is better than your previous works but still far from perfect.
I like the amount of detail on Miku. It's nice to see that you try to vector gradually more complex images. However, there's a problem with your wall. While the part with the character is quite complex, the rest of your extended version looks very empty. It's good that you added the grass but you should have also come up with some BG because the there's now too much white space in your wall.
You also use too vibrant colors and can't combine them properly. Miku's skin is too orange-ish and looks unnatural and her hair has shadows in wrong areas. Which is another problem - you don't seem to understand how lights and shadows work. You placed lights on the wall behind Miku although that area should be darker because it's covered with Miku's shadow. You also didn't add any shadows on the floor under her. Notice that even though there's mostly her reflection visible in the original scan, the shadows are there as well. The grass should also create some shadows but there's nothing in your wall.
The white lines on the floor are out of place. I know they're supposed to be water stripes to indicate that the floor is wet but you should have at least made them a bit transparent. Water isn't white, is it? Another thing is that they're just unconnected lines and look more like strange white worms than flowing water. If you want to make special effects like a wet surface, you should use various filters, edits or brushes for that. For wet surface specifically, there should be a reflection of what's in the image just like in the original scan. What is wet is also darker than dry surfaces so you could have made the whole floor dark as in the bottom right corner.
And finally - merging, blending and the overall impression. When I look at your wall, I absolutely do not get the feeling that it's raining there. You used so many bright colors that it looks like everything is covered in sunlight. The flowers above Miku literally shine. Why is there so much white on them? It makes no sense since they're in a darker area, too. The little blue, purple and pink dots have lost their meaning as well. They do not look like raindrops but like little magical lights.
When you work on a wallpaper, you should consider the overall atmosphere. Do you want to make a happy bright wall depicting a sunny day? Or create a darker, more dull atmosphere of a rainy afternoon? Always have your intended effect on your mind and try to make the elements in your wall (such as the colors, lighting effects or even the BG itself) work together to achieve that effect. Otherwise, your walls will look distorted even if you choose a pretty image/idea to begin with. Your walls have to be both technically well-made but also aesthetically pleasing. And I think that the esthetic/visual side is often more important than technical quality. You can make a technically flawless image but if it doesn't draw people's attention also visually, there won't be many viewers who'll enjoy it.
I hope it all makes sense. I don't want to discourage you but you really need to work harder and to improve to make better walls so I believe some advice could help you a lot.