You are not being selfish, by the way.
But you do have to tell your DH that you've found out and that you absolutely can't bear the thought of it. If he has any regard for your feelings at all, then he should understand and change the plans.
As a minor tangent, if there's one thing that really annoys me, it's tv shows/films that show someone saying "Oh I really don't want a party", then not getting one and throwing a strop about it. It just adds to the whole "you don't really mean it when you say no" attitude that people have; or the "oh you'll enjoy it when you get there" - No!
Some people might try to play those sort of mind games but most people, when they say they'd hate the idea, REALLY MEAN IT.
And it's hugely disrespectful to try and force someone to do something that they would hate just because you think they "don't really mean it, you'll enjoy it when you get there". Bollocks.
I know I've been a bit repetitive there but fuckit, people need to GET IT - it's NOT FUN if you hate being in the limelight, hate being the centre of attention, hate parties etc.
I had to have words with my sister about this kind of thing - my Dad and I are similar in our dislike for public displays of birthday stuff etc., but my sister and Mum both loved it. Sister was always buying huge balloons with dates on, trying to go to places like TGI Fridays and having the birthday cake and song (Oh God how I hate that) and my Dad loathed it. So the word was to say: "look, we get that you like it but Dad really doesn't and you're being really unkind to force him into that situation. You can't make people like what you like just because you think they should, it doesn't work that way".
More people could do with taking that message on board - luckily my sister did.