Directions said to cook on 325 for 30 minutes. Using 9 x 13 pan
Loosely place foil over the top to keep it from over-browning. And keep baking. :) If the temp was any higher I might say decrease the temp too, but 325 is already pretty low.
perhaps test/calobrate your oven to ensure it is baking at the correct temperature. How un-cooked is the center? Is it still like batter or just a little gooey. I'm assuming you are using the tooth-pick method of checking done-ness. I would concure with the above suggestion: loosley covering with foil and continue to bake until done.
Agree with using loose foil and lowering temperature. I would probably lower it to 300 degrees and if u see top is already quite brown u can try to turn off oven but leave the cake inside and check at ie 5 minute intervals. It has worked for me!