Take it back... get them to fix it. I wouldn't want to see that crap hanging out under my Jeep. I suspect it looked nothing like that when you took it in.

 

You got the junior mechanic working on your jeep. That's high temp silicon sealant he used.

 

It looks like they took a big slab of bologna and used it for a gasket. That's not even the right gasket maker for the differential. Not that what they used would hurt anything but back to the point.
Take it in and tell them you want it redone for free and if it isn't expanded/smooshed to the inside of the cover you will be happy to pay again and see what they say. I'm guessing they probably charged you a Benjamin for that too...