To be honest, I'm a bit clueless about this wall. The coloring work on the character is done pretty well, but the outlines are extremely bad (I see pixels!). I'm not sure if that's caused by the fact that Inkscape isn't the right program for vectors (only software like Adobe Illustrator is, although Photoshop does a fine job too at higher resolutions) or that you chose the wrong settings. Also, be more creative in vectoring or re-cg'ing a scan. There's a lot of out-of-border coloring in the original scan which you could or should have fixed, but haven't.

Same with the background: there's some good elements in it, but also some very bad. To start with the good: I like the water effect where it's shallow and where the water meets the sand. Could've been worked out a bit more subtle, but still a nice try. The sky is also OK, but the clouds in the upper part are suddenly very detailed and very opaque.
The sand, well, that's just crap. Don't ever use a noise pattern like that! Instead, just go for a smooth surface (plain color or light gradient) with vectored shadow- and wetness-effects.

And then there's the thing that you're obviously clueless about: lighting and composition. If the sun is on the top-right, how can the shadow of the girl's body and clothes be faced down-right? Plus, the reflection of the sun in the water is completely illogical.
About composition: it's more comfortable for the eye to see the character on the right side of the screen. This would also fix the faulty shadow-issue on the character, since you'd be putting the sun on the top-left in that case (in other words: the character in the scan was intended to be put on the right side as well).

I'm not trying to burn you off here, just trying to give a lot of help at once ;). You've got potention, you just need a lot of practise ;).