Why do you say that you would bomb the test? You got good grades. You were a tutor and a TA. I am a tutor myself, and a fellow tutor always says that you can only get better if you tutor. My husband used to say that you don't really know a subject till you have taught it several times. I tend to agree with both of them, and you have this advantage. For sure, I would use it if I was you.
You should be able to take it. Quit being scared and face it. You can do it. You still can retake it (many times) if it is not as good as you want it to be, or to stop the reporting of the grades to schools. So, go ahead and do it. You could do great and get accepted into the best ones.
I never took the MGRE but I have great respect for this test. I have studied for years and I have been getting better because of it. At least half of problems are easy or doable. Don't try to solve all of them. Concentrate in the one you can do. Instead of trying to solve 66 problems (or whatever number of problems there are in the test), just try to do 40 or 50, but do them really good. Time is a huge constraint. But this is like this for everybody.
While studying, concentrate on doing MGRE kind of problems by as many methods as you possibly can. The more methods you can think of, the more flexible you will get at solving them. That will help you quite a bit while taking the actual test.