Mac and Cheese disaster

So I saw a video of a guy making some real bomb mac and cheese really easily by cooking the noodles, leaving some of the pasta water in it after draining and adding cheese shredder shredded cheese to the mix. It looked really really good and I wanted to try it, so I took some nice thick Farvalle pasta and cooked it up. I saved some of the pasta water to put in there and put in shredded cheese.
Problem: the shredded cheese was (pre-prepped, store-bought) mozzarella, so it all combined into a cheese ball thing instead of like melting into a sauce thing. I tried stabbing it and then some of the pasta with a fork but it’s just.. not the same, man.
Please leave your comments. I don’t know how to make mac and cheese. I’ve been sustaining myself on Beef flavor packet instant ramen for months