How to show correct and incorrect answers to multiple answer test?

I'm in the process of converting a paper-based test to an online one. One particular test is giving me significant pause for thought. It's a multiple answer, "check all that apply" question based on a statement. The user selects the options they think apply, they show as checked. When they're done with the quiz we show them how they did, what they got wrong. This is one question in both states:

If they got it correct, it's highlighted in green. Red for incorrect. The three red options above should have been checked.
That kinda-almost makes sense for me but the client has made a few head-scratchy comments and in my experience if you have to explain how an interface works out of band, it's probably not a very good interface.

I've seen other questions on UX about multiple-option tests, and yes, it's easy enough to bung an "{in,}correct" label next to the question when there's only one option to talk about. But adding (eg) 6 labels starts to make the whole thing a little cluttered.

The way they handle this on paper is by a separate answer sheet which shows a perfect test, filled in. If we could guarantee desktop usage, we might have the space for this, but on mobile these things already fill the screen. Trying to get the user to compare between two of them seems folly.

I'm looking for good options that make this clearer. There could be a dozen options for a statement so brevity is key, it needs to work in tight situations. Accessibility is also fairly important, and probably something I'm not addressing well enough already.