Pouring self-leveling cement to a given depth
Self leveling cement is not used to raise the whole floor up to where you want it, it is for filling low spots or slopes to make the floor  FLAT. 

Take up the cement board, If it was not put down with some Thinset or adhesive, and put down the appropriate thickness of plywood so that when you put the cement board back down you have you floor at the proper height. ( OR ad a new layer of cement board to get your height.)

Fill the low spot on the sub-floor before you put your cement board back down. 

Save your nuts !