I am making my first tiramisu, using [this recipe](http://www.epicurious.com/recipes/food/views/Tiramisu-351138) from Gourmet (with high ratings on Epicurious). My mascarpone mixture looks terribly soft to me. 

As per recipe, I foamed 4 yolks with 80 ml sherry (I had no Marsala) and 95 g sugar at 55°C. The yolks were from recently bought M-sized eggs, there were no L-size in the supermarket. The volume increased a lot, but the foam itself was runny. I mixed in the 450 g mascarpone (the egg mass was still warmish), and it seemed to dissolve (I hope I didn't melt it). The result was still foamy and runny. Then I folded in the 240 g whipped cream. The final consistency is similar to egg whites beaten to stiff peaks. It is a foam, and not runny, but very aerated, and I suspect that, if left on a heap (instead of a bowl), it will flow flat over time. It is very unlike the cream layer in tiramisu I've had before. 

Is this normal? Will the cream harden in the fridge? Will the ladyfingers soak up some moisture? (They are coffee-dipped in this recipe). Or should I put in some gelatine to make sure it will keep shape? Or some other thickener? I have xanthan, but don't know how to incorporate it, the mass won't survive a mixer on full speed, and it will clump if not perfectly dispersed.