I need some advice on what to do with my mom

Okay so here’s what’s up ladies I need some advice on how I should handle my mom, so i am pregnant obviously and it was a really big surprise as I wasn’t supposed to even get pregnant and I wanted to keep the gender a secret when I found out I was pregnant so I told my mom I was pregnant because I just had to tell someone! Anyway she asked me if I was going to find out the gender and I said “no,I’m going to know but no one else will because I want to keep it a surprise” and she got all defensive saying how that’s not right and not fair and it’s just rude to not let everyone know so I caved and said well then let’s do a gender reveal... not what I wanted at all but I caved cuz I didn’t want to deal with her pestering me...my sex ultrasound is coming up soon and I still don’t want to do a gender party I feel like telling her we were unable to figure out the sex that baby wasn’t cooperating or something and then she has no choice but to wait .... in doing this does this make me a bad person for lying? 😩😩😩