Great questions!
I think that you can say that you are the DD. Which means that you are driving yourself home, and you need to be sober for this.
Keep SR close by.
Call someone for support.
Leave early if you start getting urges
If a drink is offered, take soda or water, juice.
You have nothing to explain to anyone.
Also, you can always cancel if you feel like this is too early in your sobriety.
Take care of you!!!
We are all here for support.
Also, I do not know how you will be at the party. Be yourself. Be happy that you are there. These people are friends ya?