I don't think the OP is asking whether or not to sanitize the actual hops... He's asking if the temp (while still inside the bag) will hurt the soon to be dry hops and if 2 oz of Centennial is a correct amount to dry hop with.
In answer to the first question, I assume since hop additions to the boil get 200F + temps for up to an hour or more, the heat's not going to affect them for 3 minutes, especially since they aren't exposed to the wort (or anything) at that point.
As far as how much dry hops? Well, that's kind of an interesting question. Reason is, there is no way I'm aware of of measuring or determining aroma contributions, other than taste. There are no contributions to IBU from flame out or dry hops, and no "aroma" measurement, so Beersmith or Brewtarget aren't going to change any of the numbers for flame out or dry hops, no matter how much you add.
I think someone with more experience could probably explain further, but my limited understanding is that dry hops contribute to the flavor based on the essential oils, and that alpha acid for dry hopping is typically low (4-5%), aka "Noble" hops. This guy,
http://www.winning-homebrew.com/dry-hopping.html has a good explanation. Centennial's alpha acid is normally at least 9%, so might not be a "typical" dry hop, but then again, Chinook and Columbus (the other "C's") have been used successfully according to that article, and they are typically higher in alpha acid, so you may have great results.