Hi Nunsu,
All of the simulation exams provided from these more popular companies generally provide you with in a similar range of accuracy. Typically they range + or - 30 points in reference to each other and to the actual GMAT. I would not worry as much about one lower score as there was obviously something that went wrong, whether it was stress, or just an unfortunate sequence of wrong questions answered that held greater weight than that of a previous set. Instead continue your studies, and in about a week take another practice exam. You can take one for free here:
https://gmat.economist.com/Let me know how you do on your next practice exam and what you feel your areas of weakness are. Also, when do you plan on taking the GMAT? If you have any other questions, just let me know.
Good luck with your studies!
-Evan