If your lasagna is watery it could be from two different things. First, you must salt the eggplant after you slice it to release some of the water content, and you must roast it until it softens and is getting golden. If the eggplant is still a bit raw before layering, it still has water to release, and it will make the lasagna watery. Second, be sure to cook the tomato sauce down for the full 20 minutes. We're letting water evaporate as well as concentrating the flavor of the tomatoes.