What if you continued with your sin after the baptism of water? Do you still need to be baptized again?
The proper question is whether you repented of your sins before you were baptized. Some people do want to become Christians, but they are not interested in giving up some of their sins. Since repentance is necessary before baptism, then I would encourage such a person to first repent and then be properly baptized.
However, even when the commitment to fight against sin is made and you join with the Lord in baptism, it does not mean the struggle with sin ends. "If we say that we have no sin, we deceive ourselves, and the truth is not in us" (I John 1:8). One does not need to be baptized again because he slipped up and sinned again. Rather he needs to repent of that sin and confess it to God. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9). The real point is that a Christian doesn't accept living with sin. A Christian constantly battles sin.