How do you ladies handle the stress/guilt of keeping boundaries?

I’m dealing with major anxiety right now. Tomorrow is July 4th and my family wants to go into the city to watch fireworks. I had plans with my friends that I made like a week or two ago and they told me they wanted to go today, aka the day before. My mom is fine with the fact I have plans but my sister is giving me an issue. My sister doesn’t live home so they’d be going out to her. She’s all mad at me because I’m not coming and she has to be alone with my mom and my mom’s boyfriend.

But I can guarantee if she had plans, she would blow us off. It’s always a double standard with her. Whenever she visits home, she hangs with her friends while we’re all supposed to be together but I don’t say anything because it’s her life and I don’t care. But she doesn’t have that same energy for me. So I politely said I don’t think I can come cause I have plans i made previously that I’m looking forward to. I even went the extra step to offer to make it up her like to go out to dinner soon or something but she’s just mad and keeps giving one word answers

This is making me feel so much guilt and anxiety. I’ve always been scared of my sister and I go into a spiral when she’s mad at me. Now I’m questioning whether I’m in the wrong and should just cancel my plans to go with my family. How do I keep this boundary without feeling stress? I struggle so much with this and people pleasing :(

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How do you ladies handle the stress/guilt of keeping boundaries?