I can understand what you are trying to say, but it may sound a bit better if you word it like this “My room is my calmness (or where I feel most calm). It’s neither large nor small. it’s the place where I like to rest, do my homework, and clean in. A good thing (or something I love) about my room is that it is very cozy and spacious”

Here's some options on how to fix some issues and potentially improve it further. The first re-write has minimal changes, but plenty of options, just to fix the grammar, then give you some ideas on slight variations. The second re-write has more significant changes, to be closer to something I would feel comfortable saying, as an educated native speaker. My room is my calmness / my place of calmness / my place to relaxation. It's neither (too) large nor (too) small. There I rest, do my homework, tidy up / clean up / have a wash, etc. The great advantage of my room is that/how it's (so) cosy and (yet) (so) spacious. My bedroom is my sanctuary. It's where I feel calm. It's neither too large nor too small. It's where I rest, do my homework, have a wash, and so much more. What I most love about my room, is how it's so cosy and yet so roomy, so to speak.

Your description is almost clear, but there are a few adjustments for grammar and flow. Here's a revised version: "My room is my place of calm. It’s neither large nor small. I rest, do my homework, and clean there. The greatest advantage of my room is that it’s both cozy and spacious." This version improves clarity and smoothness while keeping your original meaning.