Cream cheese icing too runny - can I save it?

[LynetteScavo]

I used full fat, added some butter, lemon juice - maybe too much?- and some icing sugar.

So, it's too runny. What can I do to thicken it?

I realise this is a zombie thread but after my cream cheese frosting turned liquid last night this thread came up on a Google search so I am posting for the benefit of other future google searches.
So my cream cheese frosting turned liquid. Like others on here I tried adding more sugar which made it worse. As it was late at night and I couldn't face the washing up I just bunged the bowl of yucky liquid cream cheese in the fridge. This morning I have come down to find it has set perfectly. I have spread it on the carrot cake and it has spread just right. It has remained solid once spread on top of the cake and looks just like the picture in the recipe book.
I have taste tested it (!) and it is delicious although possibly a bit sweet for some palates perhaps due to the extra icing sugar I added when it first went wrong. I added lemon zest not juice originally.
Enjoy your carrot cakes MNers (but possibly the day after you made them)!

I rescued mine by adding gelatine - mad a very smooth icing and didn't alter the taste. Perfect!