Is it possible to change L visa to F type

My F type application was rejected so I had to apply for L type instead. My purpose of going to China is for an exchange programme lasting for 45 days. I am aware that I have go against the nature of my visa. What should I do from here? Should I change my L type to F type? If yes, when should I apply for it? Or should I stick with L type and apply for extension? If so, my L type is for a double entry. Can you explain to me of what am I supposed to do in details? Thank you!