It is to be hoped that you will exert yourself to learn the very basic social skills needed to be an asset to a social gathering as simple and happy as a wedding.
Sorry, but I don't have much sympathy with "social anxiety" or, to use the old fashioned term, "shyness." I see it as "I'm special and others must make special accommodations for me rather than expect me to do those challenging yet ordinary things which everyone else is routinely expected to do." You know, like "Oh, you'll have to excuse from taking my turn scrubbing the shared toilet; I'm very sensitive and will puke." My response to that it "It's not like it's plutonium. Now put on your rubber gloves and deal with it. If you puke, then you just have that much more clean up to do."
It's amazing how "sensitive" people can toughen up when those around them refuse to make special accommodations for them. Of course you go to this wedding and to all weddings, funerals, and other major family events. Your conspicuous absence creates problems for others. Do your duty instead of playing at "But I'm special." You don't have to LIKE going to family weddings, family funerals, but you do need to DO it. It's not like it's plutonium.