"Obliged"? By whom or what?
You are free to choose your actions in every moment of your life. You are not obliged to put your sobriety into danger because of the expectations of friends and family. You are not obliged by convention or politeness. You are not obliged by promises that others have made for you or about you.
If you had implied that you were excited about the celebration, I'd be giving very different counsel.
You said "I'd really rather not go at all but I feel obliged."
If that is true, then you are not listening to yourself, not honoring your true wants and needs. My experience is that the value and gift of sobriety is that my life becomes true to myself; I don't want to feel trapped inside anything, I become truly brave in my quest for freedom.
If that is false, then you are balancing precariously on the edge of the precipice, because for some reason you are misrepresenting your reasons for going.
Careful, friend!
No matter what you decide, I hope that you stay true to yourself, and stay sober, because you have invested so much energy in it and it is important to you.