You should be fine... with a beer that big you will need 350 billion yeast cells which works out to 3.5 Wyeast packs or build an appropriate starter. For the dry yeast, you'll be fine with two 11.5 gram packages. Just make sure that you hydrate the yeast first.
Also, going forward use this calculator for your yeast: http://www.mrmalty.com/calc/calc.html
Good luck... a beer that big can be challenging to get it to ferment out... Chances are you just under-pitched it.



