Urination before unprotected sex is definitely not a method to be used as birth control if you are concerned about preventing an unwanted pregnancy.
You are right in mentioning that pre-ejaculate can also contain sperms which can lead to fertilization and unwanted pregnancy. This makes the withdrawal method an extremely unreliable method of birth control.
If you are not ready for pregnancy yet, then I do recommend and encourage you to speak to a doctor regarding reliable, effective and safe contraceptive methods which can be of great help for you.
You may find out more on contraceptive methods here: https://www.human.com.sg/guide-birth-control-singapore-costs-and-options
