I agree. That really wasn’t the smartest thing you’ve ever done. Why are you having sex at 15 for starters?! Then there’s the breaking of a house rule and lying to your mom. Whew!
Someone once said, “When all else fails, tell the truth.” You already know that whatever the consequences may be, it will be much worse if your mother hears what’s gone on from someone else. If you can’t get up the courage to tell her directly, write her a note or give her your letter and this response and then stick around to talk about it.
Trust is a very fragile thing. Once it is broken, it takes a long time and exemplary behavior to win it back. The beginning is to admit the wrongdoing, apologize, and take the consequences. That probably means you’ll be grounded for awhile and that your mother will be extra vigilant. The best way to show your maturity is to accept it without protest and to be the best you know how to be.
And while you are grounded, I hope you will think about what was the rush to have sex. Most girls your age don’t and for good reasons. At 15, I doubt you are ready to manage the emotions and vulnerability that go with sexual intimacy. Then there’s the reality that sex can make babies. A person who can’t face her own mom isn’t ready to be a mother herself. If you have some idea that it is necessary to keep a boyfriend, think again. Any boy worth loving isn’t going to pressure you. Instead of falling into bed, I hope you will find other ways to get to know each other and to enjoy each other’s company. You’ll be an adult for the rest of your life. Really. There’s no hurry.
I wish you well.