Just to point out--what you refer to is the old inches/gallon myth. While this is an acceptable way to determine stocking level for certain types of fish, it should not be applied to any and all fish. Small, slim bodied fish such as neons can be stocked using the inch/gallon method. For heavy bodied fish, aggressive fish, fish with large territory needs, this method falls flat on it's mythical face. Cichlids in general are aggressive, and heavy bodied, so there's no way that this standard can accurately be used.
If you can not upgrade the tank, I would return the fish now, while they are all still alive. Do some research, and find some fish that will fit into your tank happily.