Alfredo sauce "clumps' instead of being creamy. What am I doing wrong. Use 2 C s cream. 1/4 C butter and 1 C shredded Parmesan (off t

The sauce is too hot, which causes the cheese to break down. I would suggest adding a tablespoon or two of cornstarch to some of the cream, and then adding that to the cream as it heats. Then turn off the heat, and whisk in your finely shredded cheese a little at a time. If the temps are too high, the cheese will break and clump. If it starts to happen off the heat, you can also whisk in an ice cube to help reduce the heat a little. Remove the ice cube before it completely melts though, so you don't water down the sauce.

Cromis001 -
Your ingredients sound like part of a standard recipe. I'm guessing maybe something in the cooking method went wrong.
Have a look at this article about what causes clumps in sauce, and how to fix them.
https://food52.com/blog/14876-kitchen-rescue-how-to-fix-a-broken-or-curdled-sauce
If that's not enough, there are many videos on line for fixing clumpy or broken sauces.