Don't get worried, get prepared.
-Make an "escape plan". Come up with a justified reason to leave the event at any point, and make sure that you have the means to do so.
-Tell a sober friend (or your sponsor, or someone on SR) that you will be there and check in with them when you leave to let them know you are sober.
-Prepare your response for when someone offers you a drink. I prefer to say "no thanks" and leave it at that, but others feel like they need to prepare more of an explanation. "I don't drink" is a good one or "I can't because of medication". Ones to avoid are "I can't for my health" or "I'd rather not", because some people may cajole you into accepting after you say something wishy-washy like that.
-Come up with a list of reasons why you want to stay sober tonight.
-Remind yourself that you are not longer a drinker, so drinking is not an option. Period.
And don't forget the most important rule, rule number one:
If there's no pressing reason for you to attend a function with alcohol then skip it
Best wishes