If you do over-whip your cream past that soft peak stage and into the stage where it’s starting to get stiff and clumpy, there’s an easy fix: more cream! You’ll want to switch to whipping by hand to do this fix: simply pour about an extra tablespoon of heavy cream into the bowl and whisk gently, adding more cream tablespoon by tablespoon until it’s reached your desired consistency. It will actually come back from the edge.
Source: How to Save Over-Whipped Cream
When life gives you over-whipped cream, make butter 😉