GMAT Strategy

Last Saturday I took my first GMAT prep cat and scored a surprising 690. I say surprising because I have been studying for over 2 months now and have completed a manhattan gmat course- all the while my MGMAT CAT scores have been in the 600s (600, 640, 620, 640).

As I am aiming for a 700, i was thrilled to see if finally scored near a 700 on my first GMAT CAT. However, from what i've gathered from reading other posts, there seems to be a +/- 50pt variation on scores. So, a week away from my test now, I am freaking out that my 690 was merely a freak accident vs. an actual improvement.

I realize that the MGMAT quant tends to be tougher than the actual GMAT, but at this point I cannot accurately assess what my score may be, which is quite nervewracking. A 700 would make me the happiest person alive, but a 640 would force me to re-take the GMAT.

Have other's GMAT CATs been an accurate assessment of actual test performance?