Code window is a bit on the small side, and there's loads of wasted space to its right. Scrolling left/right/up/down makes it really difficult to read even trivial code samples.
If you're really clever you could let it be resizable...
However I'd vote for extending it to match the code, up to reasonable limits, obviously no wider than the browser window but it should take the browser size into account, and the length could be increased as well if need be (maybe up to a maximum of 40 lines of code?)
Attached screenshot showing at least where the code window should extend into (IMHO) :-)