Hi Enrik,
I understand what you must be feeling right now. I scored a 490 on my practice mock in late December last year. I was targeting the best possible score.
What I can recommend you to do is to leverage all the resources from the GMAT Club. I did not pay a penny and all I did was study using the plethora of questions on GMAT Club and some of the invaluable free resources such as TTP and EmpowerGMAT trials.
I made my way from 490 in my mock to 650 on the actual GMAT within 1 month of focused, dedicated GMAT prep.
Because you would be taking the GMAT again, a very useful tip I can share with you is to focus on what you DONT know. What you know is irrelevant. What you do not know is where you are going to lose points. So focus on that.
Here is a strategic take that will help you with your target score:
1. Set a score that is realistic in proportion to the efforts you are willing to put in. If 600 is your TS, then you have to make sure you get all those 500 level questions right.
2. Work your way through easy as well as mid level problems. You need to get all the basic questions in the bag so that you do not lose points.
3. Focus on quality over quantity. Clearing you concepts is more valuable than mindlessly solving 100s of questions.
4. Check out the many online practice tests you can take weekly to gauge your progress. Review questions you got wrong to figure why you got them wrong and learn from your mistakes.
5. Mock tests mean little. They are just an indicator but they are not absolute. I scored only a 560 on my final official practice test but a 650 on the actual. What will get you through to your target score is your level of preparation about various concepts, your physiological state on the test day and overall readiness.
All the best.