My younger sister saw something embarrassing on my phone..

Hey I'm a (20F) and my sister is (17F) .

me and my sister don't have the best relationship since we were younge, we always fight but for normal sibling reasons and we don't ever share secrets.

today accidentally she saw something I'm too embarrassed about on my phone and now I'm not comfortable that she knows about it and don't feel safe cuz I'm afraid she might tell someone about it.....she kept saying that she won't say anything but I'm too embarrassed that as her older sister she saw something like this on my phone ... how do I stop thinking about it or at least feel better now ((T_T))

BTW, my best friend knows about that and I'm not bothered at all, but for some reason it bothers me with my sis...