Hm, some pictures with a flashlight up to it would really help. I don't know that much about shark eggs, or what that mucus would be....
Zoodiver or other egg owners might have more info on that. Google hasn't even turned up with anything good yet... I would flash a light up to the egg and take a look at all the connections of the sac and make sure everything looked like it was hooked up right.
It could just be nothing or you could have just got a "bad egg". I hope for the best but even if its bad, theres not much you can do now. Try to monitor the egg a little more and watch for movement. As they get bigger they may not move as much due to smaller space.
Check your tempeture, water conditions, PH, make sure nothing is wrong with the tank or conditions.