My fifteen year old daughter told me she had ?

i have a fifteen year old daughter, im a single parent since im recently divorced from her father. she just told me that she had , now, i know it hat to take a lot of courage and trust on her part to be able to tell me that, my reaccion was calm, although i express my disappointment, because i had tought her better, she is not pregnant, but i am terrifien that if it happen already, it may happen again and again, and then she could get pregnant. i dont want to give her contraceptives, because to me that would be allowing her to go freely on an active life, but on the other hand, i know it may happen again and that will certainly be a risk. i know that she had to missuse the trust that i have deposited on her, because i have always been meticulous about her sleep over her friends house, always made sure that the mother would be there, and she would take them and bring them home to and from the movies, and i did the same when her friends slept over in our home. but, we all know that they will always manage to find an opportunity. well, i would like to talk to her and tell her that from now on i will be more carefull about what she does and where she goes, but then i dont want to spoil the trust that she has to tell me things, i really dont know what to do, i dont want to become the mother that because of her trust, i will accept this behavior, but at the same time i dont want to jeoperdize the level of relationship that exist between she and i. how can i avoid this from happening again without puting in risk our relationship. I really need help, i woul like to get proffesional or experiences answers please. thank you.