Runny cream cheese frosting is most likely because the ratio of cream cheese to butter and icing sugar is off. It could also be too hot in your room, so try refrigerating it for 10 to 15 minutes. If it's still not thickened after that, add a few tablespoons of powdered sugar. If it's not stable enough to frost a cake, it would be perfect for drizzling over hot cinnamon rolls.