Hi,
Have you spoke with your doctor or gynecologist about your concerns with your hymen and sex?
I have no personal experience with this, but from everything I've read and heard, most women with septate hymen's seek professional medical advice and treatment (minor surgery) before having intercourse. The reason behind having the minor surgery is so that the extra band(s) can be cut, so the vaginal opening will no longer be blocked. You should probably make an appointment with your doctor for an exam first, to find out if this is something that you need surgery for or not.
Take Care & Good Luck
Hopefully, your question will be answered here, but as far as having sex with your boyfriend, consider putting intercourse off the table for now, since at your age, you have the potential for further growth and body changes.