Whipped cream is not getting thicken properly
Is it chilled? Whipped cream whips up faster and more efficiently if everything is chilled. Have you added sugar to it already? Sweetened cream takes forever to whip.
A local baker told me that generally the problem is that most heavy cream/whipping cream is ultra-pasteurized and that makes it very difficult to whip properly. I do notice differences between brands so you may try switching.