Hi,
Heres my two bobs worth. I am not sure though exactly how this works, but a couple of points from my experience.
Firstly you're getting very close. Shooting -1 or -2 though, wont necessarily drop your rating. I am amatuer and found that I have to shoot -3 to have any real effect on ratings. I think the calculation is based on your last 10 rounds, so if you keep shooting minus figures you'll get there. Correct me people if this is wrong !!
Once you get to amateur level then you really have to start all over again. Tees go back to the Pro tees adding 20+ yards or so to the hole length. Then the wind has more effect on the ball flight. Also you start to land the ball in unusual places on the fairway - so you have to practice a fair bit. It is very easy for your rating to start to slip up - oh yeh - and theres no going back either. Once you get their thats it, and thats fair enough to.
So - get on that practice fairway, and good luck.
Cheers
Doug