Thinking of you OP. If your daughter is pregnant, she has a fantastic Mum who can be a great support.
Is it likely that your dd would hide this from you? Given that you have an open relationship usually? Has she confided in you that she and her bf were having sex?
The bit of paper could be a game that she and her friends were playing. I remember three of my friends discussing how they wanted babies after they left school. They were writing down baby names and who they would choose for the Father! (kind of like X loves x, or writing their first name with a guys surname) I told them they were crazy, but then my Mum let me babysit a relatives baby, most weekends overnight, from newborn to age three! So I knew there was no way that I was having babies, until I was married, or in a serious relationship and had enough money to afford it properly. (I am hoping that one of my brothers will have a baby when dd is a teenager, so she can learn how much work they are too!)
I would be wary of jumping the gun, as mentioned your dd may have never been sexually active. Is there a chance she would buy pads herself? Or would she perhaps get them from school?
If it turns out that she isn’t pregnant, then it would be a good time to talk about protection.
If she is, then I wish her the best, whatever she decides to do, I am sure she will still have a bright future, having a supportive Mother will make life much easier for her.