Sour Cream can sit out at room temperature for 2 hours maximum and any longer than that bacteria can grow in the sour cream causing it spoil.
If sour cream has been left out longer than 2 hours then it's likely spoiled or about to spoil.
Either eat the sour the sour cream or refrigerate before 2 hours or throw it out.
The sour cream will start to grow mold in it and get smelly and if so it should throw it out.
Refrigerate any leftover sour cream or any other dairy products within a few hours of using it or serving it.
Sour cream must always be refrigerated when it's not being served or consumed.