Well, join the club! We all have been in your shoes. Those first parties are tough: the feeling that we had to attend and couldn't say no. The awful nervousness about drinks being served, wondering what we were going to say when people asked us what we wanted to drink.
You are walking down a very well worn path.
If you absolutely feel you have to go:there are plenty of tools you can use: tried and true one's are having a quick answer why you aren't drinking and in early sobriety I had absolutely no qualms about telling a white lie: on medication, took pain killers, stomach off, etc, etc.
As I grew more comfortable in sobriety, I just said: No, thank you. And was shocked when the answer was "okay". !!!!
We have something we call the exit plan. Arrive, fulfill your social duties, say hello, but if you feel even the tiniest bit uncomfortable: leave at once. Always have your own ride and be ready to say the polite goodbyes.
We are a big fellowship of recovered alcoholics: we have all experienced what you are experiencing. You can do it! Just remember your tools.....