Am I in the wrong?

Wendy🌻 • Mommy to 4 sweet babies. 2 beautiful girls and 2 handsome boys. Baby #5 is a GIRL and due in June!!
My gender reveal is TWO days away.. 
We've been telling our family that I couldn't figure out the gender, just so they'd stop asking me what the baby is. 
I mean TWO days! Come on!
My sister texted me this morning all pissed off because I didn't tell her. 
She ruins my gender reveal with EVERY BABY! I'm not taking chances this time. 
Does she have a right to be pissed at me?