WIBTAH for only wanting my biological parents for my birthday

I (15 f) my parents divorced when I was 11 after the divorce we had 50/50 custody schedule for first year they sent me to a bording school which I insisted on and now they both have gotten remarried and I respectfully refused to attend because it was awkward but their new partner think It was not right for me to not attend their marriage so I always have a Rocky relationship with my parents's new partner what's why I only want my biological parents for my birthday