Hey Castonia! Great stuff I see you submitting, its very adventurous! I've noticed that your works are looking great conceptually, but lack a bit of color execution, especially with your value range. Below I've greyscaled some of your work and then added some contrast filtering to show more what I mean.
To solve it you could really experiment with what makes you most comfortable. Greyscaling a painting first is a good route for learning and more solid assurance it will turn out great; but you could also do some in depth color studies.
Hope this helps! I love your mermaids and hope to see more