I don't know, short of removing the water, leveling properly and then refilling. This is the one step you cannot take shortcuts on.
You have a 24' pool ~ that is a considerable amount of water and weight.
"Some blocks may be a little bit less than others" is going to be a problem: at 20" you have noticed, filling it will more likely result if the walls caving.
There are numerous posts on this site where folks have gone into great detail about how they leveled. Use the search feature and get some proven ideas from there. For safety reasons do not take shortcuts. If you, family members / friends are in the pool and it is not installed correctly and the walls give serious injury to people will result. If no one is on the pool and the walls give that water is rolling to to lowest point, it will take the path of least resistance and it could damage your home / yard. I didn't install our AGP ~ we had a contractor do it, I knew we could assemble it, the leveling though did intimidate me & for safety reasons I opted to get someone in there who guaranteed their work. Many people here have prepped their areas themselves, so I know it can be done & it can be done properly. I also know it really is key to the whole operation and has to be done precisely for safety.