I gave my GMAT yesterday and was able to score 730 with a month of serious preparation, although I used to go through gmatclub forums every now and then before that. I owe it most to
expert global tests and ofcourse gmatclub. Tests helped me gauge my performance and I actually found these tests closer to the real gmat than few others I took. My last 3 scores were 700,740,710. Most important thing is to trust the knowledge you have developed through your preparation and to not get discouraged by the low test scores. Learn and improve. All the best!