Your line quality is beautiful in this drawing. Super clean work. It's really helpful for me to lightly sketch the basic shape of what I'm drawing, like an envelope, so I can get the proportions and angles right. I made this demo to show what I'm seeing when I look at this snail in terms of simplifying to CSI, and my process. The analysis phase is really important so you can go in with a plan. Notice that in my initial sketch, I made the back half of a body a straight line, and then added a C and S curve to make it a more complex shape that better represents the reference image. I think that's the main thing that's off about your drawing -- straight lines represent stability and structure. Your drawing has few straight lines, and feels a bit like it's floating. Hope that helps, the idea is a bit abstract. You're doing great!