I kissed my twin sisters best friend?

My sisters is on a swim team and her best friend is really nice. I don't swim because I'm an actor/singer/song writer so I don't see her often but when I do go, she screams my name and gives me a big hug. We have a secret handshake too which she loves. My sister told her that our older brother was getting married but when Stephanie herd that she gies really?! And my sister thought she wS talking about me. They now have this little joke that I'm married to steph. Were 14 so it's just a little joke. I really like her. Since Lauren(my sister) is my twin, I don't tell her cus she may tell steph. We went over to her house before their team banquet and we talked a little. We sat on her bed and it was just us 3 and her head was on my shoulder. Our mom comes in and steph sqickley moves so nothing looks suspicious. They were all joking saying we really should be together cus were so similar. But the whole time Lauren was covering her ears, she couldn't think of Stephanie like that. My mom and Lauren then leave so it's just us too. We both started lying down so now she's lying down next to me with one arm around my stomach and my arms around her shoulder I'm sorta playing with her hand. We hear my mom coming so we quickly get up. When my mom went down stairs I pulled her close to me and I kissed her. She kissed me back so we stood thir like making out for like 5 minutes. It was the best 5 minutes of my life. We stopped and hugged and she looked at me a kissed me again. I want to see her more but idk what to tell Lauren.. Stephanies an amazing girl and I don't want to loose her. Idk what to do.. :(