Since we don't know the recipe you used I'm not sure how to help. HOwever
did you NOT put the bechamel/custard on yours--or did you just do it for the part you served first.
I make a wonderful moussaka and the recipe I use has a sort of "real" custard on top using ricotta and egg in it that is fabulous. If you think that topping would help, this would fit a 9X13 dish. so you might halve it. needless to say, this doesn't heat over a long time!!
Topping
*8TBS butter
*6TBS flour
*4 eggs beaten well
*1Qt. milk
*2C ricotta cheese
*1/4tsp nutmeg
Heat milk to simmering Prepare topping by melting butter, add flour and whisk, mixing well. Add hot milk stirring constantly until thick and smooth. Remove from heat, cool slightly and stir in beaten egg, nutmeg and ricotta.