She's My Mom, Not My Sister

Is it me or has anyone else been asked if their mother is their sister? Ever since I was little people would always tell my mom if we were sisters. I being the child I was, just pouted and looked away. As I grew up I still hated being called my moms sister because I didn't see what people saw, I had my dads eyes, eyebrows,nose, mouth, even the same birth marks as him in the same places as him, so, what did people see that made me look like my mom? I found out that I have my moms round face and me being a girl with the same hair as her I started to see it when I started going into my preteens. I always found it mortifying that I looked like my mom, I never knew why but as I grew up I started to appreciate it because she is a beautiful woman that created me.