Coffeebean, if you have been studying for 6 months and understand everything as you say (this means you should be scoring AT LEAST 80% accuracy on your practice problems), then your problems are most likely anxiety related.
The trick to staying calm during the LSAT is to standardize your study habits. Take your practice tests and do your practice problems sitting in the same seat, at the same time, every day. Do the same things. Make it routine enough that when you sit down to take the test, you don't even have to think about it. You should be able to "snap" in and out of LSAT mode. Don't accept a 149 as the lowest you can go, just keep at it! And you should probably skip the Feb LSAT, it won't do anything but hurt you in the long run, and Feb is too late to apply for next cycle anyway.