['65 chevy lover]

I attempted to remove the freeze plug. On the 2nd wack with the hammer, the entire back of the plug popped off and fell into the block and, I was unable to retrieve it. I was able to remove the round piece of it without problems. So now what do I do? Can the flat piece remain in there without causing problems? I posted couple pics of the round part of the plug although they are kinda hard to see.