You’re getting there! 
I think you could do it darker on the bottom though.
I also use the free version of Canva sometimes. I think in Canva, there’s a way to darken or make lines clearer? If you go to Edit Image and if you click on Adjust, there’s a way to increase “Shadows” which will, hopefully, only increase the shaded parts of the bottom photo. Then you might adjust “Clarity” or “Highlights”.
It’s good if you’re just starting out that you mess around with all the adjustments you can make to see what each of them do. Slide that dot to the highest and the lowest and see what they do. Experimentation is key to improving 
If you’d like, I have a critiquing service where we can talk a little more about the cover instead of using a lot of space here. If I can get a more overall idea of where you want to go with it, I think I can give a few nudges and I’m pretty familiar with Canva 
(and the limitations of the free version 
)
Here is the place.