I believe Kaplan offers a free CAT on their website that you can take.
Manhattan GMAT has tests you can purchase although they're not CAT's, in other words, they're not adaptive. I think you might be able to buy Princeton Review CAT's on their website.
It's great that you worked through the
OG, that's a crucial part of getting a feel for the questions. But I think I'll echo others here and say that taking practice tests is really important.
A lot of people on these forums (myself included) discovered that its one thing to do practice problems, but it's another thing to take a timed test and to understand how to budget your time, how to deal with the stress of running out of time, how to get a feel for the test. It's important to be prepared for the mental fatigue that you experience when you spend an hour on the AWA, then take the quant, and then the verbal.
This might not seem like a big deal but for a lot of people it is the hardest part. Some people will do very well on practice tests and then bomb the real thing because the nerves get to them. So it's important to take as many CAT's as possible so that you are very comfortable with the timing and the format.
If you haven't taken any tests yet then you should get going. I think March 5th is doable, but as Lepium suggested if you are not doing well on the practice tests, then you should postpone your test.
One other thing, you might know this already, but it is possible to take the GMATPrep (the official test makers' tests) multiple times and get mostly new questions. Some people will take the GMAT Prep tests three times and they say that they only encounter a few repeat questions. So let's say you take each GMATPrep three times, you download the free Kaplan test, and you can get your hands on a couple others you should be in good shape.
Best of luck!