Chu Peihan didn't ask that because she planned to cheat on Han Chenglin. Since she decided to be Han Chenglin's girlfriend, she would be loyal to him as long as he treated her seriously, but she wasn't sure of Han Chenglin's feelings.
She trusted him, but she wasn't him. She couldn't control his mind, so she was still very careful even though Han Chenglin liked her very much.
Since Han Chenglin wasn't in the capital, Hao Ran and the others didn't insist. They could just have fun by themselves.
However, at about 5 pm, Han Chenglin called Chu Peihan and told her that he was back in the capital. He would arrive at about 6 pm, so he asked if they could have dinner together.
Chu Peihan then said that she was with Gu Ning and their other friends from City F, but if he didn't mind, they could share a meal.
Han Chenglin was more than willing to hang out with Chu Peihan's good friends. It was a good thing if he could be accepted by her circle.