I don't know what to say to her?!?

so just recently i was talking to my mom when she brought up the subject of how her friend was upset because she just found out her daughter is gay. my mom doesn't know that i have an interest in girls and guys (im a girl) and i thought it was the perfect opportunity to tell her. but right when i was about to tell her first i decided to test the waters and i asked her what she would do if i was gay. and she said "i would be very disappointed in you and i would want you to know that you were going to hell" so now i don't know what to do! if i tell my mom im bi she's gonna believe im going to hell?! i don't want to be a disappointment to her but i feel like im hiding the real me when she has always taught me to be myself, what do you think i should do?