rear end leaning to one side

i have just fitted my banded steelies to my mk1 citi both rear coilovers are set to the same hight yet it still sits lower on the left, can i just set the coilovers at the heights to make the car sit level or could i shim the top mount with a plate to compensate for the sag ? or is there a way to sort it out properly. also gettin paranoid that i may have a front spring in the back could this be a possiblitiy?

i suppose it is possible, do they have helper springs to? could be different lengths also.
if the fronts are level though id say something else.
do you have the bushes all mounted the right way?
did you measure from the spring platforms themselves?