Thank you for your answers... Hjort, you're right, I'll try to take the test on the scheduled day, after all I have time before the final week to decide rescheduling.
Well Eddie Cruiser, when I took the practice exam (530) I had finished reading Kapplan and Princeton, and had about a week doing practice questions from OG.
I recently took another practice exam a week after the other and I scored 560 (

well at least it's an improvement).
I do fairly well on the math section but RC and the two Essays are my weaknesses (take me a lot of time). I am trying to read a lot (business articles, summaries, etc.) to get used and read and write faster.
I still have questions:
I was thinking of buying the book “Answers to the Real Essay Questions“ by Arco or subscribing to ETS’s “Essay Insightâ€