Why my chocolate ganache not harden?

Recently made chocolate tartlets, and the filling I used was

110g cooking chocolate 125ml heavy cream

I melted the chocolate and used bain marie method for heavy cream. Recipe mentioned hot so i let it sit until it was hot for my fingers to touch. Then i mixed it in the chocolate. I poured immediately in tart shell.

After 30 minutes in freezer it still wasn't cool so I let it sit in there overnight. Next day I took it out and it still not harden. In fact, after a bit it became liquid again. What have i done wrong?

Sorry for English not my native language