I have been in similar situations and was able to abstain...but, it was a big challenge. I took on the event as such...a challenge. And, I have also failed miserably under such challenges, at times.
Honestly, you would be doing yourself a big favor by finding a reason not to go. What is worth more, a "party"....or the rest of your life? You may not want to be "shamed" for not going...but when you are really sober, you will wear this like a badge of honor. And those who really care for you will see your action as a strength, not a weakness.