It's hard to gauge a body with missing limbs xP
I'm not so great with cartoon animal bodies myself. I agree that it's currently looking unbalanced, but fortunately it's unbalanced due to another problem: That's not a beaver body. Beavers are quite bottom-heavy, and they have those big flat tails. You did a good job with the head, but for the body you just drew a generic fat cartoon animal.
Here's
a reference photo that I think will be particularly useful. This is a young beaver (young = cute = probably closer to what you want in a cartoon version), standing upright. Look at how wide the hips are relative to the rest of the body, and how there is no distinct neck. Look at how large the feet are, and now they're webbed.
There are plenty more references out there. Look at them. Figure out what makes beavers look like beavers, and exaggerate that.