Your anxiety is completely understandable, and I think the limits you are setting hit a pretty good balance. In truth, most adolescents already "know" whether they will restrain their natural, growing interest in and curiosity about sex. I've known lots of teens (and I was one of them) who comprehend that its more physically and emotionally wise to wait until you meet the person you want to spend your life with.
If your daughter has come to that understanding (presumably with your consistent counsel and example as she's matured), she'll probably hold to her internalized boundaries with or without your rules about how much privacy is allowed. If she hasn't learned that deep respect for herself by now, it's not too likely that any intervention by you will ultimately stop sexual activity, in which case making sure she has access to birth control is a good Plan B.
It's hard to get this about our precious children, but truthfully, if they have sex, they are not ruined, or even that drastically changed. If they get an STD, that's harder, but they are still not ruined, they need additional medical care. If they get pregnant, they are STILL not ruined. Their lives change dramatically, yes. But it's really only our perfect parental pictures about who and what they are, and what their lives "should" or should not include, that get ruined. And, of course, we worry about our reputations as parents getting ruined.
But our children, by the time they are 15 or so, have a tendency to head off in their own unique directions, with their internal compasses shaped not only by us, but by a million other influences, many invisible to us.
That's the shakeup parents really fear. It can be helpful to realize that your worries, valid as they are, are at least as much about you as about your daughter. If you love her (and I have no doubt about that – no implication otherwise), then your best course forward will be to keep communication honest, open, and understanding.
There are lots of good books out there to help guide parents through these years. I personally never stop reading and harvesting the wisdom of others. My best to you. You sound like a terrific mom.