Chicken Manicotti

I changed the recipe a little bit because after going to 3 stores I couldn't find manicotti shells. So I boiled the chicken and shredded it. Stuffed it with Spaghetti sauce, mozzarella cheese and Italian seasoning. I filled the shells and put in disposable tins. The freezer recipe said to do uncooked shells. I am wondering if this turned out well or not. I though next time I should cook them a little bit. When I cooked them the shells were a little harder than I would have liked.
Here's the recipe written from the Girlfriends cookbook:
2Tbsp olive oil
1 Tbsp garlic powder
1 1/2 lbs. boneless skinless chicken breasts
10 uncooked manicotti shells
1 Jar of spaghetti sauce
1 can of mushrooms
2 cups shredded mozzarella cheese
2/3 cup water

cut chicken in 1 inch strips and brown in olive oil and garlic powder. spread 1 cup spaghetti sauce in pan. stuff chicken into uncooked manicotti shells and place on top of spaghetti sauce. top shells with mushrooms and pour remaining sauce over top. sprinkle with cheese. pour water aroudn the edges of dish. cover and bake at 375 for 50-60 minutes.

if freezing cover with plastic wrap and then foil. Remove plastic wrap and recover with foil before baking.