My stepsister challenges me that I won't be able to last 10 minutes without cumming in her hands

My horny stepsister challenges me saying that all men ejaculate very fast, in my case it's the opposite, but I couldn't hold back seeing her tits and her big ass sitting on my cock, it's so white and fleshy, her swollen pussy, she was right, I came before 10 minutes and it made my hard cock empty on her