to have second thoughts about (something) (to start having doubts about [something] which you originally thought was good)
A: I thought studying science at university was a good idea, but now I’m having second thoughts about it. I can’t understand the lectures at all.
B: You should talk to your professor about it. He will be able to help you.
A: Helen had second thoughts about climbing Mt. Fuji when it started to rain heavily.
B: Had she started climbing?
A: No, she was just about to start.
Can you make a sentence using “have second thoughts”?