Am I being disrespectful to myself?

I’m 15 years old and I have a sister who is 26 years old and i also have a boyfriend. My boyfriend and I kiss and that’s it we don’t have sex or anything because well we’re both 15 and that’s just a bit too young. Now my big sister says that when we kiss I’m disrespecting myself. I’m just not sure how I’m disrespecting myself. So if you guys think that I am could you please tell me how? Or it you think that I’m not please tell me too but my sisters opinion really matters to me and I want to be sure that I didn’t get mad at her for nothing