Hmm, I've never had a problem. The boss battle should initiate as soon as you attempt to light the candle up that last staircase. You lit all the candles up to this point, right?

If the boss battle doesn't start when you try to light the final candle up the last stairs my recommendation would be to go back to the very beginning and go very carefully through once again making sure to light up all bloodstones and candles.