Please add a spoiler warning in the future. You gave a lot away there.
Spoiler below.
*
*
*
*
*
*
*
*
*
*
*
Sounds like you took too long. Phaerie (sp?) blows your cover if you take too long between starting after the blood and the ceremony. (The one the matron is using your blood for). I never had this problem, but you might want to look back into the temple. If I recall, the gates are opened when the matron dies, she MIGHT be n the chamber off to the left. That is where the ceremony might have taken place.
In the worst case, you can console your way out. I forgot the area code for the underdark, but I think it is 2301,2401,2501 or something like that. Just save your game and experiment. I still recommend finding the matron if at all possible. You have already put a lot of sweat into the game to get this far and it would be a shame to cheat and ruin it now.
------------------
- Cayle