If you're a native English speaker, there's no reason why you shouldn't be able to improve verbal significantly with a little work. It sounds like you're going to get your MAC, which means you can't be completely Quant illiterate either, so I see no reason why you can't bump that up either with some targeted studying.
Also, if you are planning to go to business school, I would highly recommend getting your dream score now. You will be so mad at yourself if in three years, you realize you're applying to business school, didn't get the score you wanted/were capable of, and have to start over basically from scratch. Plus, as bad as studying is when you're a student, it's even worse after 12+ hour work days (you're going to be a CPA after all...), so if I were you, I'd try to get it out of the way ASAP.
1. For SC, it sounds like you started with the MGMAT book
. That's great. I would go a step further and using that book, develop a specific framework that you apply to every single SC you get. Whatever is easiest for you as you read, but basically a 4-step checklist where you said "1) Subject-Verb, do they agree? 2) Parallelism, good or bad?...". You should do this for the original sentence, identify problem areas, and then go to work splitting the answer choices and everything else that they suggest. Then, in the end, apply your exact same checklist for your final answer before clicking it. From the people I have talked to (and myself), most English speakers don't have issues with Verbal timing, so you should have time to do all of this.
2. I broke this out, but DO NOT use your ear for SC until you've exhausted every rule you know and can't decide between the final two choices. Try to eliminate based on hard grammar rules (e.g. your checklist).
3. Study RC and CR strategy. You might be decent at them, but if you're able to improve your SC (which you will), you'll start getting much harder RC and CR questions, where it becomes much more important to have a strategy. While i never took notes like MGMAT suggests, they do have some decent tips for how to attack each type of questions, and I would recommend at least having a loose strategy for both of these when the questions get tough.
4. Study MGMAT Strategy Guides WITH OG problems. The books will lose 90% of their usefulness if you simply read them, and then move on to the next one. Read one, do every in-action problem, then do every official guide problem associated with that topic. When you can't figure one out, really try to work through it before looking at the answer (and definitely don't worry about time at that point). If you still can't get one, or get it wrong, look at the right answer, but not the explanation. See if you can figure out how to get that right answer now that you know what it is. If you can't, then look at the first step of their explanation, and see if you can solve it from there. Never just look at the answer and be done.
5. Once you have done every topic book, it's time to start with CATs and Error Logs, and go back to strategy books/the official guide where you need to (problem areas). This will also be the time to start thinking about timing (on your CATs).
6. If you're planning to take the test in August, you need a study plan for Integrated Reasoning too. I can't help you there, but just something to think about.
I could go into far more detail, but I would think that you could be a much higher scorer with some more, targeted work. My debrief probably has some more useful advice if you want to look there.