ESR Analysis and the most effective 4-week study plan

Hopefully any of the experts can help me provide further details on my analysis of the ESR and help me create a study plan!

I've studied for around 11 weeks, of which the last week very intensive. I scored a disappointing 490 Q35 V23. I want to challenge myself a little bit and I'm aiming for a score of at least 580, although I only need a score of 550 to get into the first Dutch University (others in Holland ask for a minimum score of 600). The first 10 weeks I followed a course on the University where I hope to begin my Master Marketing in February. On every Monday evening we did Quant (3h) and on Wednesday evening we did Verbal (3h) during the course. These lessons began after I worked the whole day at the office. Besides that, I went one day per week to the library to study from 10 AM to 5 PM. The last week I took a week off from work and studied everyday (except the last day) from 10 AM to 5 PM.

Verbal:
I'm not a native English speaker since I'm Dutch. I have traveled through Asia for a half year and haven't had a problem there with my English language. During the course there was a lot of attention for Sentence Correction. I did this part pretty well on my practice exams and answered most of the questions correct. However, according to the ESR, I scored really bad on my Sentence Correction. Before I started my real GMAT test, I thought RC was my biggest weakness. I think I score average on the CR questions.

I'd like to aim for a score V27-28.
1) To get a higher Verbal score it is important to increase my speed whilst reading RC passages and make RC questions in general, the problem is that I don't see how to attack these kind of questions as quickly and efficiently as possible.
2) The second area is to improve on are the SC questions. I know the fundamentals of the grammar rules and I know some shortcuts to answer these question 'quickly', but I do not know why I scored so bad on these questions during my real test.
3) (CR) Sometimes I find it difficult to determine if one of the answers is correct or out of scope. Maybe this has something to do with determining the main clause?

Quant:
I've always been pretty good at Quant (strange enough). During the course we practiced a lot of questions, but little GMAT type questions (mostly open questions, no multiple choice). Especially in my last week I tried a lot of Easy and Medium questions from the Official GMAT Guide. Easy was often easy for me, Medium did go okay (6/10). I did not try a lot of Hard questions. Maybe this was one of the problems? I can see in my EDR I scored really good in the first part, then the difficulty level increased, and I failed in the last part (4/4). I still think Arithmetic (Counting/Sets/Series) is my biggest weakness, as you can see in the ESR. What could be the best way for me to improve this? Making more Difficult questions? During my test, I felt confident because I knew I was answering questions on a Medium/High level. Unfortunately, I failed the last part of the questions. I think this had a major negative effect on my Quant score (because I was answering questions incorrect in a row). Maybe I rushed a little in the end, but time management was not the problem.

I'd like to aim for a score Q42. (average of three practice exams was Q33)
1) It is clear that Arithmetic in its entirety is my biggest weakness. Although I think I know the rules, I still make many mistakes. Sometimes these are Easy questions where I make sloppy mistakes. How can I improve this?
2) When analyzing my ESR, there is a little difference between PS questions and DS questions. Are there any suggestions on test-taking strategies for DS questions?

My next attempt is in 4 weeks. Since I have to score 550 before the 10th of January (deadline study registration), I want to try this in the begin of December. If I would fail again, I can try it one more time before this deadline date. Although this sounds like a short time and I work four days a week, I've taken some vacation days and have about 80-90 full hours of studying available before retaking the GMAT.

Hopefully you have some suggestions regarding my study plan after the above stated information and a look at my ESR I attached to the message. I'm really wondering what my most effective 'battle-plan' is so that I can get the most out of my GMAT-score, since I know I have a pretty good score in me.

Thanks in advance!

Remco