Dessert flopped,

yesterday I decided that after out steak meal we would have a new dessert and made a lemon and meringue cake all was good I even made the lemon curd, ( I made this for the first time without a recipe as most of my cooking is so I don't have a recipe to add). that tasted good anyway the Ida is to make a thin sponge and then put the meringue on top and cook well I forgot the butter for the sponge and it need to be really soft so I got the butter out of the fridge and put it in a bowl and in the microwave for 30 seconds, it came out melted so I scrape the batter that I had put in the tin already and add the butter. it was to runny so I put in the freezer for 5 min to thicken a little but not hard top it with halve the meringue mix add put in the oven. Everything was going well until time to put together, the meringue sunk, I whipped the cream a fraction to much and the top meringue sunk too. my husband asked so you made this instead of lemon meringue pie? end result it tasted good kids ate it up and Ian went back for seconds. ( sigh of releif).