Loss and val loss too big
It could be normal to have such large loss value if your predicted values are far from the ground truth values (because of the square in the mean squared error loss).
Try to print the predicted values and ground truth with tf.Print to check that.
You can normalize your ground truth values so that their range is not too big. For example it should be easier for the network to predict values between 0 and 10 than values between 0 and 1000.