There’s a trick you can do to tell if the inside is fully cooked. Take the lasagna out of the oven. Take a metal butter knife and stick it right in the middle of the lasagna so that it stands upright. Leave it there for about 15 seconds. Then take it out and feel how hot it is. It must be very hot for the medium to be made.
Additionally, you should bake the lasagna, covered with foil, until the last 10 minutes or so. It can barely burn if you do. Spray a little Pam on the side of the foil that touches the lasagna so it doesn’t stick.
Cook the lasagna with the aluminum foil and check the cooking with the knife test. When it’s cooked in the middle, remove the foil and bake uncovered until the top is golden brown to your liking.