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I do not believe that the fact that you have not been re-baptized means that you have not repented. I see it as simply being confusion based upon not being sure when you were saved. If you truly received Christ the first time, then baptism is not necessary. If you were not saved until the second time, then baptism is necessary.
Only you and God know the answer to the question of when you were saved. My suggestion would be that you ask God for the answer, and then seek the answer from His direction in His Word. James tells us that if any man lack wisdom, "let him ask of God". In this instance, you need wisdom concerning the time of your salvation. I believe that God, through His Spirit and through His Word, can reveal that to you.
If you remain uncertain, then I would recommend that you get re-baptized. Perhaps you are bothered by this because the Holy Spirit is convicting you, and if that is the case, then you need to get re-baptized.
Either way, you need to get this settled so that you can move forward in your Christian life.
Hebrews 6:1-2 says,
"Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God, Of the doctrine of baptisms,...".
If we are going to move on to maturity and completeness, we have to get passed salvation and baptism. If you know that you are saved, praise the Lord. If you aren't sure, then you need to trust God for salvation or trust Him for assurance. Once you are certain of your salvation, then you need to be sure that you have been baptized by immersion since your conversion. Get those two things taken care of, and you will be on your way to the fullness of the Christian life.