What's a good excuse to not attend a bridal shower?

Hey ladies, so my boyfriends sister is getting married in late April and she is having her bridal shower tomorrow. I am looking for a good excuse to not attend because I have social anxiety and I get really nervous around people I don't know. Another thing is that I really don't know his sister that much and we haven't really taken the time to get to know one another. I know I may get heat on this post but I just feel really uncomfortable... What can I do to get out of this situation?? By the way, I am trying at all costs to not hurt her feelings. ☺️