Gender reveal ultrasound

Okay . Heres a hopefully quick story . My boyfriend said he wanted his mom to come with us to one of the ultrasound appointments . I said hmmm . Sure . He said she would really appriciate it . I like his mom and all , we actually became close . Well one day i was just a happy little camper and saw her and she was rubbing my belly blah blah blah , and i got too excited and told him to ask her if she would come to the gender reveal ultrasound . (she is spanish so i couldn't ask) At 18/20 weeks or whatever . Well ever since i found out i was pregnant and decided to keep the baby , i have wanted to have a gender reveal little gathering because everyone in his family kept saying i want to know right away . I'm like alrighty haha (i have no family besides my sister) .... Well now i have been regretting asking her to come because i wanted it to be a REALLY special thing between me and my boyfriend to find the gender out just me and him . I had a moment of weakness and was stupid to have him ask his mom before i completely thought it out . I mean his sister has two kids and his mom is really involved with their life . So its not like she hasn't been to ultrasounds. i was thinking i would ask her to come with me to the 14 week one , and just have my boyfriend tell her i'm sorry that i asked before and are changing my mind but i really just want this to be a secret between me and him for right now and announce it to his family all at once . Would i be wrong for that ? Any advice how to word that to my boyfriend without sounding like a bitch . 😩