We had to take down the same pool for the same reason. Our backyard is also on a slope and I did almost the same thing although our soil is very sandy. I removed dirt from one side and added it to the other. We were also about 3" off.

After we took it down I borrowed a laser level from a co-worker. Its one of those that spins around. I used one of the white legs to be able to see the line and walked all over the area checking. I had to remove more dirt from the side that was high and more in the area that was low. I actually let the low side be about 1" higher when checked with the laser level to account for settling.

When we filled it this time, the water level was within 1" all around. Hope this helps...