After buying store bought pizza sauces and not being too satisfied with them, I usually just make my own sauce now. It's really easy and cheaper.
I saute grated onion and minced garlic in a little olive oil and then add a large can of store bought tomato sauce. Then add sugar and Italian seasonings, as you did (dried oregano, dried basil, salt, pepper, etc. (not sure about the rosemary though)). I have found that it needs the sugar to cut the acidity...not enough to make it too sweet though. Another thing that I think is pretty important is crushed red pepper...again, not enough to make it hot, just to add some additional seasoning. It adds a lot, IMO and though not evident (heat wise) when in the sauce, is missed when not.
After the tomato sauce goes in a pot add a teaspoon of sugar, a pinch of this and a pinch of that and taste until you've got the flavor you want, adding more pinches as needed. Let it simmer for a 1/2 hour or so and you're done.