The knock was swiftly followed by a gentle creak as the door opened slowly,
"Come on in!" he called out
I see! Thank you for clarifying. In that case, here's a revised starting point:
As soon as Lora walked into the room, Darren's eyes met hers.
In that case, here's a rephrased version that omits the dialogue:
"Oh Lora!" Darren's face fell as he realized his mistake - he had left Lora behind when he headed home the other day, without even thinking about the fact that she was waiting for him.
"Umm, I apologize for….," Just then Lora stopped him.
"Oh, no need to apologize, I completely understand," Lora said with a wave of her hand. "I knew you had a lot on your plate.
Please, don't worry about it," she added, gesturing to the chair opposite Darren as she asked, "May I sit down?"
"Sure, please do," Darren said, nodding in response to her gesture and motioning to the chair opposite him.