So while I personally have put this down to a discrepancy within the book-to-movie transition, I want to hear other alternatives.
Its been a while since I read Mockingjay but from what I remember, someone within Katniss's time in District 13 explains that the underground facility was set up a refuge from the Capitol government should it ever be needed in a time of crisis. Yet a little further on, both within and without the movie, Peeta warns them that they are about to be bombed.
Now this is where the problem arises, In the movie, Coin says comes to the conclusion that the Capitol bombers don't know what or where to bomb and are just guessing. This isn't discussed within the book.
Yet, if the underground facility was for the Capitol/Government, then why wouldn't they have detailed plans and so know exactly were to bomb them?