Do you need to heat the cream before you add it to the butter/sugar, carmel? When I added the cold cream, the carmel hardened. Thoughts?

It's always a good idea to heat cream before adding it to any sort of caramel for exactly the result you encountered. You have more cream than caramel, and the former caused the latter to cool rapidly. You should be able to rescue it, though, by reheating the cream and caramel together so that the caramel re-melts.