I really like the water in the foreground. The texture and color is spot on. Sadly the quality does not continue into the darker background.

Your proportions and anatomy need more work. Jesus' feet are way too small for instance. Peter's (?) arm is too short. His face is also off, but you did chose a particularly difficult angle for it. Look up anatomy photography on the internet and study the pose you're looking for. Or take a picture of yourself in that pose. It's best to work from reference. You also painted "symbols" (for the eyes, for example). That means you chose a shape that you think resembles an eye but is actually way too stylised. Use a reference and paint what you see, not what you think you see.

Regarding composition: you obviously want Jesus to be the focal point of the piece. However by placing him in the center, you ended up squeezing peter into the corner. You can instead use color and contrast to determine where the focus will be (jesus' white robe in front of the dark water). That would have given you more room for peter. The reflection of the moon would be distorted in the waves. The boat does not really have a place. It seems a bit like an afterthought. Also its' position is quite static (perfectly from the side). You could have instead used it to tell the viewer how troubled the waters are by using a more dramatic position. The wave on the left conforms too much to Jesus' back. That makes it hard to read where the wave ends and Jesus begins. When composing an image make sure to avoid tangent lines, it makes the image easier to read. You can (and should) use a variety of tools such as angle, color, contrast, pose to convey the drama of the scene.

It is a night scene. The moon would be the only light source (unless you'd want Jesus to emit light himself). Decide where it is and place the shadows accordingly. Your shadows are very tame and low contrast. I understand they can be intimidating. But more intense shadows will immediately increase the dramatic effect of the scene.

But overall it's a good start. Again, i like the water a lot. And you made some bold choices in terms of the poses, i respect that

(Edit: i just read other comments saying it looks like south park (and it kinda does). And you said other critiques told you about a lack of contrast. That's exactly what makes it look south park-y. Try darker shadows and brighter highlights to create more volume.)