After that she and my father both sat down with my boyfriend and I and talked about our actions we agreed not to do that again. But lately my mom keeps bringing up that situation and says mean little remarks and comments and one day she got upset with me for something and blurted out that I am a "slut". I’m still a virgin and that really hurts my feelings. How can I make her stop treating me this way?

I’m very surprised that your mother would use such language about you. If you were to believe that your parents had so little respect for you, the likelihood would be that you might go further with your boyfriend, rather than to hold back in order to keep their respect. What you were doing was probably age appropriate, and while I can understand your parent’s concern, especially because they don’t want you to go even further than you did, she should know you better. That she was angry about something else may be a partial excuse, but that is a very strong word to use about your daughter, even in anger. There may be more to her reaction than simply what she caught you doing, and I am not going to speculate what that may be. What’s important is that you not allow this to affect your actions and that you and your boyfriend not do anything out of anger or resentment. 

As to getting your mother to stop treating you this way, I might suggest that you talk to some other adult, like a grandmother or aunt, whom you would feel comfortable with and whom your mother respects. Maybe they could help your mother to realize that you are not that terrible word your mother used because of what you and your boyfriend were caught doing.