I spent yesterday afternoon making a chocolate espresso trifle. Bought what I thought was enough double cream for the top (was a bit bleary eyed in the supermarket first thing on Monday morning) but it turns out I needed 450ml and I only have 300ml. Nowhere is open here today to buy more. If I add a bit of whole milk will it still whip up? Otherwise the cream layer on the top is going to be very thin!