I need help. I have to come out but I'm terrified.

Over the weekend my mom got new SIM cards for our phones. While activating them, they switched our phone numbers. SO SHE WAS GETTING MY TEXTS. I'm a teenage girl, I have secrets my mom shouldn't fine out, including my sexuality. Anyways, I fixed the problem, but now my mom is suspicious of me. She turned on iMessage so she receives all of my messages along with hers. I panicked, thinking one of my friends would text me about a girl I like, so I turned off all iMessage and unlinked myself from our iTunes. My mom got mad, and I just keep telling her it's the new SIM card being weird...

So I've decided I better come out before she finds out by snooping. I'm terrified about it, but I'll feel better knowing I was the one who told her. Here's my plan:

My school has a 4 day weekend that starts February 14th and ends on the 17th. I will write a letter explaining everything. That I'm bisexual, but more homoromantic. That I've dated and kissed guys (she doesn't even know I've kissed a guy..) as well as dated and kissed girls. I'll talk about how I've hated myself for over a year, but have learned that it's okay. I will explain my acceptance and how I hope she accepts me too. I'll tell her I'm sleeping over at a friends house for the night and leave the letter on her bed. Then I'll spend the 4 day weekend staying at different friends houses so my mom has time to think about it and digest it.

Does this sound like a good idea? My mom is strict Irish catholic and conservative. She doesn't support gay rights... I just really like girls and can see myself with a girl more than a guy. I know I can't say it to her face because I tried to tell my sister and I couldn't even do that. I'm scared to tell her and how she will react, but I'm also scared she'll find out before I get the chance to tell her.

HELP???