Hey massimassi,
It might feel terrible to not be able to see the desired result even after you put in a lot of effort. But dont worry. I too kind of am in the same boat and looking at your score, I realize that you are lagging behind in quant which is pulling your score down. Your verbal is above average and I would recommend that you keep hold of your current verbal by regular practice but try to strengthen your fundamentals in quant.
I am no verbal expert but I can share some wisdom on quant. One thing in quant is that it is after all about formulas and rules. Once you ace them, you are good to go.
So start with fundamentals and keep revising them before you attack any question. You must realize that your scores are definitely reflective of your practice tests. ( +- 30 is common ) so always aim for your target score +30 on your practice tests.
As you are saying that you were able to finish on time but your scores are low so that means your accuracy is less than what is required. So start practicing each topic separately and analyze what are your weak areas and strong areas and how are the accuracies moving with each practice session.
This way you will learn the tips and tricks and see the hidden patterns in the question types and realize not every question has to be treated differently. After all it's a standardized test.
note down what all patterns you are able to notice and keep revising them regularly so that you get mechanical next time you see a similar pattern in a question.
But remember the official content is very limited so utilize it religiously. There is no point in taking 100 mocks till you are not strong with fundamentals. You need not solve 100 problems to learn a concept. You can solve a problem in 10 different ways and still learn most of the concepts.
Lastly, it maybe the case that you are falling for the trap answer choices so every time you judge an answer choice start double checking whether you have missed any loop holes. You can apply substitution method for many PS questions, you can practice elimination strategies. So keep all of this in mind and think whether you are really able to apply all these concepts or not.
Also there is also GRE if you are targeting for an MBA, GMAT is not the only exam so keep an open mind and validate other options as well. As I heard GRE quant is easier. So might as well look into it.
AS you are targeting SLOAN which is a highly competitive program and you need a score of 730+ at least in my opinion (I am no expert so verify with an expert on what should be your target score for the respective university, given your background).
So your aim should be 750+ in mocks so that you reach your target score in the test. Do not write the exam till you reach our mock target coz you are just wasting your attempts otherwise.
So take time introspect what is wrong and restart your journey.
Good luck!! I am sure you will rock it this time!!