Finally Said No, then said Yes

Back in June, my 15 year old boyfriend asked me if I wanted to have sex. Being the idiot I was then, I allowed it. Today, he started messing with my breasts and sticking his hands down my pants and I stopped him. I told him I didn't want to do that and he asked me why. I told him I didn't feel comfortable doing that again, especially after what happened last time. He kept asking and started begging but I stood my ground and refused. He eventually quit, but later gave me a request (which was really weird). He requested that when I see him, most likely tomorrow, that I wear a dress and nothing underneath. Unfortunately, idiot me took over and agreed. He gave me a promise bracelet and made me promise to not tell and to follow his request. Idiot me promised. I made this post anonymous so nobody I know will realize who I am. I'm slowly learning to say no, but I'm still struggling. I don't know what to do though. I don't want to wear a dress with nothing under it. And I really don't want to have sex again. I'm only 15. I don't want to make the same stupid mistake I made back in June.

Update: We broke up, but he got what he wanted that day.