One thing.
I noticed you mentioned ballooning... Now i am not an expert on the topic but i did had some major issues controlling RPM at the end of the auto and flaring, and my instructor said this had been made more difficult because of my weight... I was near the top of the limits in RPM and sometimes a bit over them and everytime i flared (i usually don't touch the collective at the flare until i bleed some airspeed) but in my case i balooned and the RPM got way high, and if i pull collective i will baloon even more. So the way i could control RPM was by having the RPM on almost the bottom of the green (WELL WITHIN LIMITS), and when i initiate the flare i don't touch collective, and i baloon a bit. I also come in a bit slower than usual but within limits (ALLWAYS WITHIN POH LIMITS), and at then end when i bleed airspeed, i pull a bit collective to stop forward movement, then level and then cushin.
However my instructor did not noticed this until i ask him to demonstrate this to me again, cause i was having lots of trouble, and when he tried it he went (WWOOOAA) that was unexpected. And we both mastered a techniq that was within limits at all times but mostly refine the timing of my reactions for my weight, and we tried this with different fueling to get a feel for reaction, but mostly in the top of the limits the auto felt very very different than from the lower part... The thing is the flare and balooning with high weights.
I know i will get a lot of rocks here saying "YOU HAVE TO FEEL THE AUTO, INDEPENDANT OF THE WEIGHT" well that's true, but i was just a beginer following instructions from an instructor expecting something to happen, and it did happened but happened completely different from what he was expecting, so he blamed it on me, when it was on the timing... So we fixed this and then experimented with diferent weights (fuel) to get a feel for reactions.
So what i recommend is DO one auto. Then let the instructor do one, and then do one together. And then try one. And so and so.. Its practice...
I think you can make your goal if you stop worring on how fast you need to make the test; You'l be ready sooner than you think...
RELAX...
HAVE FUN....
AND ENJOY.....
And you will make it... I swear...