Why do you think it isn't clean? Because of the rust? I think that fridge is fine. The plant is not really stretching much and is not going to fill that rack all the way up now. A bigger box will just be overkill. Unless you are having heat issue I would stay in the fridge.
Don't be discouraged because the screen isn't filled up. There is a learning curve to every new strain you grow. You have to find out how much they stretch, especially when you do scrog. That way you can accurately predict when to flip them to 12/12.
I didn't realize you had switched to 12/12 at first. Otherwise I would have told you to at least fill the screen half way before you 12/12 them. I want to see you become the mini-fridge scrog master. So hang in there.
