Holidays can be stressful

Holidays can be stressful I was recently invited to a christmas dinner by my boyfriend's step-sister. From what I hear it'll be most of his family and some of thier friends. Ever since the invite my anxiety has been through the roof thinking about it. I want to somehow get out of it because since covid my stutter has become severe and I can barely get out a sentence. I am so afraid I'll embarrass him and myself.