OK guys, (And gals!) Where did I go wrong with this recipe?

Here's the recipe: 1T. er, 1# cooked shrimp, 4 cloves minced garlic, 1C. half and half,6T grated parm, chopped parsley, salt &pepper to taste. I sauteed the garlic in the er, added the cream and slowly mixed in the cheese.(Fresh cheese) The darn thing would NOT thicken. Also, I used 1/2# shrimp and 1/2 # scallops. I added more and more cheese trying to get it to thicken with no luck. The only thing I can think of is I used frozen packaged shrimp and scallops. Is the water content that much higher in frozen? (They were thawed, by the way). The flavor was excellent but I like it much thicker...Any ideas?