That wasn't technically true. She hadn't been ready to sleep with Puck, so telling Finn that she hadn't been ready wasn't really a lie. Though she could see now how he thought it might be. After all, she wasn't a virgin anymore. She hated that fact more than anything. If her parents found out, they would kill her. She would not only be overthrown as president of the Celibacy Club but probably also kicked out. The church would probably use her as an example... Especially since it wasn't just a case of having sex, but also cheating. As much as she hated that word, it was the truth and she knew it.
"I wasn't ready, Finn," she said softly. "Not with you, not with Puck, not with anyone." She sighed softly and closed her eyes. She really hoped she wasn't going to have to tell him what had happened that day. It seemed a little personal and it involved a lot of insecurities. She never liked admitting her insecurities. She was pretty sure that Finn didn't even know what went on in her head most of the time. "I don't think you want to hear what happened that day," she tried, hoping he would let it go at that, "but I never meant to cheat on you."
Quinn didn't entirely know what she hoped to gain from this. She knew that she couldn't apologize and have Finn just take her back that easily. Did she hope that they could get back together at some point? Yes. She knew it would take a lot of work on her part trying to regain his trust, but she wanted a chance to try.