This is normal.
How are you doing on full-length practice tests? That will be your best indicator of whether you should postpone. I would say if you are scoring more than 10 points under your target MCAT score, on AAMC tests, you need to figure out what's going on and perhaps reconsider. (if you're one of those diligent people shooting for a 40, ignore above and just keep working hard) If you are shooting for a 30 and are still scoring under 25, it is too early to make the call on postponing, but you need to keep working hard and efficiently.
It is best to avoid freaking out. You just keep studying and telling yourself, I am going to do my best. I cannot learn everything perfectly, but I will do my best. This situation will come up over and over again in first year of med school and you will have to go into exams feeling woefully unprepared.
Make a list of problem topics as you work through the science content. Highlight the most problematic. Know that you will never have enough time to review all of them, but at least try to tackle a few of the worst per week (e.g. lenses, focal length, etc.) and really learn them properly.
Be sure that you are not leaning towards studying the stuff you already know well, and avoiding your problem areas. This is an easy trap to fall into.
Keep doing MCAT-format practice passages and tests (instead of 1001-style), even if you have not finished reviewing the content. Use these to help identify problem areas in content and strategy. You should be doing full-lengths at least every second Saturday by now.
Be sure to keep checking your timing on passages. You need to know that you can finish a science passage in 7-8 minutes and a verbal in 9. You can always go back after the allotted time and try again to answer the questions (BEFORE looking at answers is most effective!).
Make sure that you review and analyze your wrong answers on PS and BS sections. Figure out if you are consistently making math errors or other simple errors such as not reading the passage or questions properly.
shahab - you need to figure out a way to find more time for life as well as studying. If you can't cut back your work hours, something else needs to change. Again, how you are doing on practice tests is a useful indicator.
good luck