Withdrawal intercourse on the 21st day is there any possibility of pregnancy?

There is just as much of a possibility of you becoming pregnant if the man had ejaculated inside of you because there is pre-ejaculate, I am sure, that was inside of you. Pre-ejaculate contains sperm as well. If you are not ready to become pregnant then I would suggest you either get on birth control or he use condoms. The withdrawal method is about the most ineffective way to prevent pregnancy.