As written before in this thread: it is gone, that is one sin erased by the Grace of God.
So, what now? First you need to, or at least try to, understand that we all sin. That is why we have Confession. What you did is of course wrong, but you will not do it again I think, so don’t worry about that. And what about your future marriage someday? Does she really need to know? Honesty is always the best way, but in some cases it is wiser to keep mum. What someone don’t know will not hurt, yes? Your only problem is that if she ask you must tell the truth, but IMO only if she ask, and why would she? Maybe if she have the same problem. And if the worst happen, and she ask you, keep in mind that she love you enough to marry you so a mistake in the past will not change a thing, and if it do, don’t marry her. I know many will tell me what I am because of this answer and advice and they are most likely right, but I try to be realistic with life. We do sin, we are not perfect and love that will end in a confession about “have you ever…” is not love at all. (You don’t need to follow my advice.)
If you would know how much I have done your small flaw is nothing. All my life I have had, and have still, a very strong faith, never a doubt, not even in the darkest hours of my life so far, but I did lose my virginity (sounds stupid to call a boy/man “virgin”, in Finnish we have a special word for a boy/man who have had sex and lose the “virginity”, direct translation is “boyhood”) age fifteen and before I did marry there was many girls and women I had sex with and even if I knew it was a sin I have also always have faith in a God who love and forgive. But I am not totally rotten, I did stop having sex shortly after my divorce in 1994, and I was not a Catholic then, that happen first 2002. So your small mistake is not as bad as you think. People on forums like this, and this is the best forum I have been told, are not always as good Catholics as they like to let other members understand. To be a Catholic is a tricky thing, and sometimes pretty unfair, but as our Bishop did say, rewarding anyway in the end. So I would suggest that you continue to seek for a wife, and tell the truth is she ask, and if that will end your relationship/marriage it was far from real love. We all carry baggage at this age so…we must accept that we are not perfect, and it is enough, I hope, for God that we try to be, He will understand, and as in the song: “He say He understand and well done”, meaning that He know we sin, and if we repent it is OK. If this matter really bug you confess it, even though you don’t need to. God bless you and keep in mind that we all are sinners.