First, I copied this into Photoshop and Photoshop is telling me your scan is light. So, I adjusted it to what Photoshop (and I) believe your original actually looks like (below left).
It's still on the pale side - everything is rather ethereal and semi-transparent - so I darkened it a little more.
MOUSE1015-Mouse.jpg
Then I discovered a very light hand and arm appearing beneath the chin. I think that's important to the story you're telling, so I darkened that to give it some solidity and presence. As a bonus, it now emphasises the bottom of the mouth, which pushes the arm back.
I think you have two problems:
At your stage you're almost certainly having to think about technique. Working out
how to do something, rather than why you might want to. And that gets in the way. So, don't worry about that - just keep drawing and you'll soon learn all the basics and no longer have to think about them.
And you're probably looking at drawing in reverse - concentrating on the detail without asking yourself where that detail is. Try the other way round. Asks yourself why you want to draw it. What is it that you want to show to your audience? What is important to your story? How can you bring that story to life? Now you'll be working with a plan and reality foremost in your mind rather than the detail. You still need the detail, but you'll be aware of where it is - round the back in the shade, on top and in full light, and so on.
What missing from your drawing is light and shade, and it's those that describe three-dimensional form. Omit them, or pay them little attention, and your drawing will be perfectly detailed but flat - and probably a bit lifeless too.
And don't forget the props
Those ears of wheat, or whatever they are, could do with some light and shade too.