Vegetable lasagna a bit too wet. How to adjust baking temp/time?
Mushrooms can throw off excess moisture.  I would suggest cooking them down a bit further and draining on paper towel before adding them to your lasagna.  You didn't mention how you baked your lasagna, but my process is to bake (and your temp is fine) covered for 40 to 50 minutes.  Then to uncover and return to the oven for about 10 to 15 minutes more.  I'll take a look, and often run it under the broiler to brown the top and crisp the edges.