Have you tried twisting it just a little to get it to come free and then pulling it?
Yes, that’s most likely the case.
What about using some oil?
Any sort of oil should be OK. Placing a cotton pad soaked in oil all over the back and keeping it there for a few minutes can help to absorb up the excess oil. This should soften the back a bit and even cause it to grow a little, perhaps returning the hole back to its original dimensions. It’s likely that it took some time to dry out, so you’ll simply have to bandage the cotton with the oil on it overnight to give it enough time to do its job.