It happens!
I bought the OG about 2 yrs back, prepared on and off. Lost track so many times! Then in July this year, I decided enough was enough and I booked my GMAT date for August. Took it too lightly and one week before my GMAT, I postponed it to September. After that, I focused totally on prep and I think it worked out well for me in the end!
I'd suggest don't worry about it. Make a good study plan and start preparing. Book your GMAT date 2-3 weeks after you start prep. I think 2 hours a day(a little more than that on the weekends) for around 2 months should help you do well on the GMAT. Let me know if you have any more queries!
My GMAT score: 740 [Q:48, V:42]